From d56f8e1c0f75e7865c8259ec58528a812087959b Mon Sep 17 00:00:00 2001
From: Marcel <marcel.lang15@googlemail.com>
Date: Tue, 10 Nov 2026 15:43:39 +0100
Subject: [PATCH 1/5] Add a theme switcher to the sidebar and fix black text in
 dark mode

The sidebar button cycles Windows, Light and Dark; the choice applies at once
and is kept in window.json. The SidebarLink, ChoiceCard and Switch styles now
set their own Foreground: replacing Fluent's implicit style let the classic
theme's black text show through on dark backgrounds.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 src/OrthoStreamXP/Gui/App.xaml.cs             |  1 +
 src/OrthoStreamXP/Gui/AppTheme.cs             | 54 +++++++++++++++++++
 src/OrthoStreamXP/Gui/MainWindow.xaml         | 10 ++++
 src/OrthoStreamXP/Gui/Theme.xaml              |  8 +++
 .../Gui/ViewModels/MainViewModel.cs           | 23 ++++++++
 tests/OrthoStreamXP.Tests/AppThemeTests.cs    | 39 ++++++++++++++
 6 files changed, 135 insertions(+)
 create mode 100644 src/OrthoStreamXP/Gui/AppTheme.cs
 create mode 100644 tests/OrthoStreamXP.Tests/AppThemeTests.cs

diff --git a/src/OrthoStreamXP/Gui/App.xaml.cs b/src/OrthoStreamXP/Gui/App.xaml.cs
index c4e43ba..858f194 100644
--- a/src/OrthoStreamXP/Gui/App.xaml.cs
+++ b/src/OrthoStreamXP/Gui/App.xaml.cs
@@ -25,6 +25,7 @@ protected override void OnStartup(StartupEventArgs e)
         Log.Configure(LogOutput.None, null);
         DispatcherUnhandledException += OnUnhandledException;
         _main = new MainViewModel();
+        _main.Preferences.Theme.Apply();
         var window = new MainWindow(_main);
         MainWindow = window;
         window.Show();
diff --git a/src/OrthoStreamXP/Gui/AppTheme.cs b/src/OrthoStreamXP/Gui/AppTheme.cs
new file mode 100644
index 0000000..b453f63
--- /dev/null
+++ b/src/OrthoStreamXP/Gui/AppTheme.cs
@@ -0,0 +1,54 @@
+using System.Windows;
+
+namespace OrthoStreamXP.Gui;
+
+/// <summary>The window's colours: the same as Windows, or always light or dark.</summary>
+internal enum AppTheme
+{
+    System,
+    Light,
+    Dark,
+}
+
+/// <summary>The sidebar's theme button: what it shows for a theme, and which theme a click switches to.</summary>
+internal sealed record ThemeChoice(string Label, string Glyph, AppTheme Theme)
+{
+    /// <summary>The themes in the order a click goes through them.</summary>
+    public static IReadOnlyList<ThemeChoice> All { get; } =
+    [
+        new("Windows theme", "", AppTheme.System),
+        new("Light theme", "", AppTheme.Light),
+        new("Dark theme", "", AppTheme.Dark),
+    ];
+
+    public static ThemeChoice Of(AppTheme theme) => All.FirstOrDefault(c => c.Theme == theme) ?? All[0];
+
+    /// <summary>The theme after this one, back to the first after the last.</summary>
+    public ThemeChoice Next => All[(IndexOf(Theme) + 1) % All.Count];
+
+    private static int IndexOf(AppTheme theme)
+    {
+        for (int i = 0; i < All.Count; i++)
+            if (All[i].Theme == theme) return i;
+        return 0;
+    }
+}
+
+internal static class AppThemeExtensions
+{
+#pragma warning disable WPF0001 // WPF's Fluent theme is marked experimental.
+    /// <summary>The WPF Fluent theme mode for the choice.</summary>
+    public static ThemeMode ToThemeMode(this AppTheme theme) => theme switch
+    {
+        AppTheme.Light => ThemeMode.Light,
+        AppTheme.Dark => ThemeMode.Dark,
+        _ => ThemeMode.System,
+    };
+
+    /// <summary>Switches the running application to the theme; the window's DynamicResource brushes follow.</summary>
+    public static void Apply(this AppTheme theme)
+    {
+        if (Application.Current is { } app) app.ThemeMode = theme.ToThemeMode();
+    }
+#pragma warning restore WPF0001
+}
diff --git a/src/OrthoStreamXP/Gui/MainWindow.xaml b/src/OrthoStreamXP/Gui/MainWindow.xaml
index 419800c..8fe8c29 100644
--- a/src/OrthoStreamXP/Gui/MainWindow.xaml
+++ b/src/OrthoStreamXP/Gui/MainWindow.xaml
@@ -66,6 +66,16 @@
                     </StackPanel>
                 </Button>
 
+                <!-- Theme: each click goes to the next one (Windows, Light, Dark) -->
+                <Button DockPanel.Dock="Bottom" Style="{StaticResource SidebarLink}" Margin="4,0,4,0"
+                        Command="{Binding ChangeTheme}" AutomationProperties.Name="{Binding Theme.Label, StringFormat='{}{0} (click to change)'}"
+                        ToolTip="Switch the window's colours: same as Windows, light or dark.">
+                    <StackPanel Orientation="Horizontal">
+                        <TextBlock Style="{StaticResource Icon}" Text="{Binding Theme.Glyph}" Width="20" />
+                        <TextBlock Text="{Binding Theme.Label}" Margin="12,0,0,0" VerticalAlignment="Center" />
+                    </StackPanel>
+                </Button>
+
                 <ListBox ItemsSource="{Binding Navigation}" SelectedItem="{Binding SelectedNav}"
                          ItemContainerStyle="{StaticResource NavItem}" Background="Transparent" BorderThickness="0"
                          AutomationProperties.Name="Pages" ScrollViewer.HorizontalScrollBarVisibility="Disabled" />
diff --git a/src/OrthoStreamXP/Gui/Theme.xaml b/src/OrthoStreamXP/Gui/Theme.xaml
index 876aee5..ae7db94 100644
--- a/src/OrthoStreamXP/Gui/Theme.xaml
+++ b/src/OrthoStreamXP/Gui/Theme.xaml
@@ -8,6 +8,11 @@
     <gui:VisibleWhen x:Key="Visible" />
     <gui:EqualsParameter x:Key="Is" />
 
+    <!--
+      A Style set on a control replaces Fluent's implicit one, so the classic theme's black text would show through:
+      the styles below set the Foreground themselves.
+    -->
+
     <!-- Text -->
     <Style x:Key="PageTitle" TargetType="TextBlock">
         <Setter Property="FontSize" Value="28" />
@@ -116,6 +121,7 @@
 
     <!-- A sidebar link: looks like a navigation item, but opens a web page -->
     <Style x:Key="SidebarLink" TargetType="Button">
+        <Setter Property="Foreground" Value="{DynamicResource TextFillColorPrimaryBrush}" />
         <Setter Property="Margin" Value="4,2" />
         <Setter Property="Cursor" Value="Hand" />
         <Setter Property="FocusVisualStyle" Value="{DynamicResource DefaultControlFocusVisualStyle}" />
@@ -140,6 +146,7 @@
 
     <!-- A choice shown as a card (quality presets, detected folders): an accent border when chosen -->
     <Style x:Key="ChoiceCard" TargetType="RadioButton">
+        <Setter Property="Foreground" Value="{DynamicResource TextFillColorPrimaryBrush}" />
         <Setter Property="Cursor" Value="Hand" />
         <Setter Property="FocusVisualStyle" Value="{DynamicResource DefaultControlFocusVisualStyle}" />
         <Setter Property="Margin" Value="0,0,0,6" />
@@ -196,6 +203,7 @@
 
     <!-- An on/off setting as a Windows 11 toggle switch: its text ("On", "Off") on the left, the switch on the right -->
     <Style x:Key="Switch" TargetType="CheckBox">
+        <Setter Property="Foreground" Value="{DynamicResource TextFillColorPrimaryBrush}" />
         <Setter Property="Cursor" Value="Hand" />
         <Setter Property="MinWidth" Value="0" />
         <Setter Property="VerticalAlignment" Value="Center" />
diff --git a/src/OrthoStreamXP/Gui/ViewModels/MainViewModel.cs b/src/OrthoStreamXP/Gui/ViewModels/MainViewModel.cs
index 06d5873..3a6c336 100644
--- a/src/OrthoStreamXP/Gui/ViewModels/MainViewModel.cs
+++ b/src/OrthoStreamXP/Gui/ViewModels/MainViewModel.cs
@@ -1,4 +1,5 @@
 using System.Text.Json;
+using System.Text.Json.Serialization;
 using System.Windows.Input;
 using OrthoStreamXP.Setup;
 
@@ -25,6 +26,10 @@ internal sealed class WindowPreferences
     /// <summary>Download a mesh region's roads, forests and buildings (its overlays) with it.</summary>
     public bool DownloadOverlays { get; set; } = true;
 
+    /// <summary>Light, dark, or the same as Windows.</summary>
+    [JsonConverter(typeof(JsonStringEnumConverter<AppTheme>))]
+    public AppTheme Theme { get; set; }
+
     public static WindowPreferences Load()
     {
         try
@@ -79,6 +84,7 @@ public MainViewModel()
         _selected = Navigation[0];
         HandleProblem = new RelayCommand<ProblemAction>(Handle);
         Donate = new RelayCommand(() => Shell.Open(AboutViewModel.DonationPage));
+        ChangeTheme = new RelayCommand(() => Theme = Theme.Next);
         Mount.PropertyChanged += (_, e) =>
         {
             if (e.PropertyName == nameof(MountController.State)) Raise(nameof(SidebarStatus));
@@ -140,6 +146,23 @@ private set
     /// <summary>Opens the donation page, from the sidebar.</summary>
     public ICommand Donate { get; }
 
+    /// <summary>The sidebar's theme button: Windows, then Light, then Dark.</summary>
+    public ICommand ChangeTheme { get; }
+
+    /// <summary>The window's theme: applied at once and remembered for the next start.</summary>
+    public ThemeChoice Theme
+    {
+        get => ThemeChoice.Of(Preferences.Theme);
+        private set
+        {
+            if (value.Theme == Preferences.Theme) return;
+            Preferences.Theme = value.Theme;
+            Preferences.Save();
+            value.Theme.Apply();
+            Raise();
+        }
+    }
+
     public void Show(IPage page) => SelectedNav = Navigation.First(n => n.Page == page);
 
     /// <summary>Called when the window has opened: setup on the first run, otherwise the auto-start.</summary>
diff --git a/tests/OrthoStreamXP.Tests/AppThemeTests.cs b/tests/OrthoStreamXP.Tests/AppThemeTests.cs
new file mode 100644
index 0000000..cec4e47
--- /dev/null
+++ b/tests/OrthoStreamXP.Tests/AppThemeTests.cs
@@ -0,0 +1,39 @@
+using System.Text.Json;
+using System.Windows;
+using OrthoStreamXP.Gui;
+
+namespace OrthoStreamXP.Tests;
+
+/// <summary>The window's theme choice: what each entry switches WPF to, and how window.json keeps it.</summary>
+public sealed class AppThemeTests
+{
+#pragma warning disable WPF0001
+    [Fact]
+    public void Each_choice_maps_to_its_wpf_theme_mode()
+    {
+        Assert.Equal(ThemeMode.System, AppTheme.System.ToThemeMode());
+        Assert.Equal(ThemeMode.Light, AppTheme.Light.ToThemeMode());
+        Assert.Equal(ThemeMode.Dark, AppTheme.Dark.ToThemeMode());
+    }
+#pragma warning restore WPF0001
+
+    [Fact]
+    public void Each_click_goes_windows_light_dark_and_back_to_windows()
+    {
+        ThemeChoice choice = ThemeChoice.Of(AppTheme.System);
+        var seen = new List<AppTheme>();
+        for (int i = 0; i < 4; i++, choice = choice.Next) seen.Add(choice.Theme);
+
+        Assert.Equal([AppTheme.System, AppTheme.Light, AppTheme.Dark, AppTheme.System], seen);
+    }
+
+    [Fact]
+    public void The_theme_is_kept_by_name_and_older_files_without_it_follow_windows()
+    {
+        string json = JsonSerializer.Serialize(new WindowPreferences { Theme = AppTheme.Dark });
+
+        Assert.Contains("\"Theme\":\"Dark\"", json, StringComparison.Ordinal);
+        Assert.Equal(AppTheme.Dark, JsonSerializer.Deserialize<WindowPreferences>(json)!.Theme);
+        Assert.Equal(AppTheme.System, JsonSerializer.Deserialize<WindowPreferences>("{\"AutoStart\":true}")!.Theme);
+    }
+}

From 4d4f1237d0dfe0edc7acd07bed95d5cd3e61978c Mon Sep 17 00:00:00 2001
From: Marcel <marcel.lang15@googlemail.com>
Date: Tue, 10 Nov 2026 15:52:20 +0100
Subject: [PATCH 2/5] Make the theme button switch only between light and dark

The window follows Windows until the first click; the button shows the look
Windows gives (read from AppsUseLightTheme) and each click switches to the
other one, which is then kept in window.json.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 src/OrthoStreamXP/Gui/AppTheme.cs             | 46 +++++++++++--------
 src/OrthoStreamXP/Gui/MainWindow.xaml         |  4 +-
 .../Gui/ViewModels/MainViewModel.cs           |  8 ++--
 tests/OrthoStreamXP.Tests/AppThemeTests.cs    | 16 +++++--
 4 files changed, 44 insertions(+), 30 deletions(-)

diff --git a/src/OrthoStreamXP/Gui/AppTheme.cs b/src/OrthoStreamXP/Gui/AppTheme.cs
index b453f63..5ca4fe5 100644
--- a/src/OrthoStreamXP/Gui/AppTheme.cs
+++ b/src/OrthoStreamXP/Gui/AppTheme.cs
@@ -1,8 +1,9 @@
 using System.Windows;
+using Microsoft.Win32;
 
 namespace OrthoStreamXP.Gui;
 
-/// <summary>The window's colours: the same as Windows, or always light or dark.</summary>
+/// <summary>The window's colours: the same as Windows until the person picks light or dark.</summary>
 internal enum AppTheme
 {
     System,
@@ -10,28 +11,22 @@ internal enum AppTheme
     Dark,
 }
 
-/// <summary>The sidebar's theme button: what it shows for a theme, and which theme a click switches to.</summary>
+/// <summary>The sidebar's theme button: what it shows for the current look, and the look a click switches to.</summary>
 internal sealed record ThemeChoice(string Label, string Glyph, AppTheme Theme)
 {
-    /// <summary>The themes in the order a click goes through them.</summary>
-    public static IReadOnlyList<ThemeChoice> All { get; } =
-    [
-        new("Windows theme", "", AppTheme.System),
-        new("Light theme", "", AppTheme.Light),
-        new("Dark theme", "", AppTheme.Dark),
-    ];
+    public static ThemeChoice Light { get; } = new("Light theme", "", AppTheme.Light);
+    public static ThemeChoice Dark { get; } = new("Dark theme", "", AppTheme.Dark);
 
-    public static ThemeChoice Of(AppTheme theme) => All.FirstOrDefault(c => c.Theme == theme) ?? All[0];
-
-    /// <summary>The theme after this one, back to the first after the last.</summary>
-    public ThemeChoice Next => All[(IndexOf(Theme) + 1) % All.Count];
-
-    private static int IndexOf(AppTheme theme)
+    /// <summary>The choice for a theme; the Windows one shows as the look Windows gives it.</summary>
+    public static ThemeChoice Of(AppTheme theme, Func<bool> windowsUsesLight) => theme switch
     {
-        for (int i = 0; i < All.Count; i++)
-            if (All[i].Theme == theme) return i;
-        return 0;
-    }
+        AppTheme.Light => Light,
+        AppTheme.Dark => Dark,
+        _ => windowsUsesLight() ? Light : Dark,
+    };
+
+    /// <summary>Light after dark, dark after light.</summary>
+    public ThemeChoice Other => Theme == AppTheme.Light ? Dark : Light;
 }
 
 internal static class AppThemeExtensions
@@ -52,3 +47,16 @@ public static void Apply(this AppTheme theme)
     }
 #pragma warning restore WPF0001
 }
+
+/// <summary>Whether Windows shows apps light or dark (Settings > Personalisation > Colours).</summary>
+internal static class WindowsTheme
+{
+    private const string Personalize = @"Software\Microsoft\Windows\CurrentVersion\Themes\Personalize";
+
+    /// <summary>True for light apps, also when Windows does not say (older versions default to light).</summary>
+    public static bool AppsUseLight()
+    {
+        using RegistryKey? key = Registry.CurrentUser.OpenSubKey(Personalize);
+        return key?.GetValue("AppsUseLightTheme") is not int value || value != 0;
+    }
+}
diff --git a/src/OrthoStreamXP/Gui/MainWindow.xaml b/src/OrthoStreamXP/Gui/MainWindow.xaml
index 8fe8c29..8a8d08e 100644
--- a/src/OrthoStreamXP/Gui/MainWindow.xaml
+++ b/src/OrthoStreamXP/Gui/MainWindow.xaml
@@ -66,10 +66,10 @@
                     </StackPanel>
                 </Button>
 
-                <!-- Theme: each click goes to the next one (Windows, Light, Dark) -->
+                <!-- Theme: the Windows one at first, each click switches between light and dark -->
                 <Button DockPanel.Dock="Bottom" Style="{StaticResource SidebarLink}" Margin="4,0,4,0"
                         Command="{Binding ChangeTheme}" AutomationProperties.Name="{Binding Theme.Label, StringFormat='{}{0} (click to change)'}"
-                        ToolTip="Switch the window's colours: same as Windows, light or dark.">
+                        ToolTip="Switch the window between light and dark colours.">
                     <StackPanel Orientation="Horizontal">
                         <TextBlock Style="{StaticResource Icon}" Text="{Binding Theme.Glyph}" Width="20" />
                         <TextBlock Text="{Binding Theme.Label}" Margin="12,0,0,0" VerticalAlignment="Center" />
diff --git a/src/OrthoStreamXP/Gui/ViewModels/MainViewModel.cs b/src/OrthoStreamXP/Gui/ViewModels/MainViewModel.cs
index 3a6c336..38b65b4 100644
--- a/src/OrthoStreamXP/Gui/ViewModels/MainViewModel.cs
+++ b/src/OrthoStreamXP/Gui/ViewModels/MainViewModel.cs
@@ -84,7 +84,7 @@ public MainViewModel()
         _selected = Navigation[0];
         HandleProblem = new RelayCommand<ProblemAction>(Handle);
         Donate = new RelayCommand(() => Shell.Open(AboutViewModel.DonationPage));
-        ChangeTheme = new RelayCommand(() => Theme = Theme.Next);
+        ChangeTheme = new RelayCommand(() => Theme = Theme.Other);
         Mount.PropertyChanged += (_, e) =>
         {
             if (e.PropertyName == nameof(MountController.State)) Raise(nameof(SidebarStatus));
@@ -146,13 +146,13 @@ private set
     /// <summary>Opens the donation page, from the sidebar.</summary>
     public ICommand Donate { get; }
 
-    /// <summary>The sidebar's theme button: Windows, then Light, then Dark.</summary>
+    /// <summary>The sidebar's theme button: switches between light and dark.</summary>
     public ICommand ChangeTheme { get; }
 
-    /// <summary>The window's theme: applied at once and remembered for the next start.</summary>
+    /// <summary>The window's look (the Windows one until a click picks one): applied at once and remembered for the next start.</summary>
     public ThemeChoice Theme
     {
-        get => ThemeChoice.Of(Preferences.Theme);
+        get => ThemeChoice.Of(Preferences.Theme, WindowsTheme.AppsUseLight);
         private set
         {
             if (value.Theme == Preferences.Theme) return;
diff --git a/tests/OrthoStreamXP.Tests/AppThemeTests.cs b/tests/OrthoStreamXP.Tests/AppThemeTests.cs
index cec4e47..11a90ac 100644
--- a/tests/OrthoStreamXP.Tests/AppThemeTests.cs
+++ b/tests/OrthoStreamXP.Tests/AppThemeTests.cs
@@ -18,13 +18,19 @@ public void Each_choice_maps_to_its_wpf_theme_mode()
 #pragma warning restore WPF0001
 
     [Fact]
-    public void Each_click_goes_windows_light_dark_and_back_to_windows()
+    public void A_click_switches_between_light_and_dark()
     {
-        ThemeChoice choice = ThemeChoice.Of(AppTheme.System);
-        var seen = new List<AppTheme>();
-        for (int i = 0; i < 4; i++, choice = choice.Next) seen.Add(choice.Theme);
+        Assert.Equal(AppTheme.Dark, ThemeChoice.Light.Other.Theme);
+        Assert.Equal(AppTheme.Light, ThemeChoice.Dark.Other.Theme);
+    }
 
-        Assert.Equal([AppTheme.System, AppTheme.Light, AppTheme.Dark, AppTheme.System], seen);
+    [Fact]
+    public void Until_a_click_the_button_shows_the_look_windows_gives()
+    {
+        Assert.Same(ThemeChoice.Light, ThemeChoice.Of(AppTheme.System, () => true));
+        Assert.Same(ThemeChoice.Dark, ThemeChoice.Of(AppTheme.System, () => false));
+        Assert.Same(ThemeChoice.Dark, ThemeChoice.Of(AppTheme.Dark, () => true));
+        Assert.Same(ThemeChoice.Light, ThemeChoice.Of(AppTheme.Light, () => false));
     }
 
     [Fact]

From 5ae9bceec13f6e3613d6abaa4865ed751e48ffe1 Mon Sep 17 00:00:00 2001
From: Marcel <marcel.lang15@googlemail.com>
Date: Tue, 10 Nov 2026 19:07:23 +0100
Subject: [PATCH 3/5] Let the theme button switch back to following Windows

Clicks go Windows theme (follows Windows), then the opposite of Windows' look,
then Windows' look kept fixed, then the Windows theme again, as asked in the
review of #13.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 src/OrthoStreamXP/Gui/AppTheme.cs             | 23 ++++++++++++------
 src/OrthoStreamXP/Gui/MainWindow.xaml         |  4 ++--
 .../Gui/ViewModels/MainViewModel.cs           |  8 +++----
 tests/OrthoStreamXP.Tests/AppThemeTests.cs    | 24 ++++++++++++-------
 4 files changed, 37 insertions(+), 22 deletions(-)

diff --git a/src/OrthoStreamXP/Gui/AppTheme.cs b/src/OrthoStreamXP/Gui/AppTheme.cs
index 5ca4fe5..42feb26 100644
--- a/src/OrthoStreamXP/Gui/AppTheme.cs
+++ b/src/OrthoStreamXP/Gui/AppTheme.cs
@@ -3,7 +3,7 @@
 
 namespace OrthoStreamXP.Gui;
 
-/// <summary>The window's colours: the same as Windows until the person picks light or dark.</summary>
+/// <summary>The window's colours: the Windows theme (follows Windows), or always light or dark.</summary>
 internal enum AppTheme
 {
     System,
@@ -11,22 +11,31 @@ internal enum AppTheme
     Dark,
 }
 
-/// <summary>The sidebar's theme button: what it shows for the current look, and the look a click switches to.</summary>
+/// <summary>The sidebar's theme button: what it shows for a theme, and the theme a click switches to.</summary>
 internal sealed record ThemeChoice(string Label, string Glyph, AppTheme Theme)
 {
+    public static ThemeChoice Windows { get; } = new("Windows theme", "", AppTheme.System);
     public static ThemeChoice Light { get; } = new("Light theme", "", AppTheme.Light);
     public static ThemeChoice Dark { get; } = new("Dark theme", "", AppTheme.Dark);
 
-    /// <summary>The choice for a theme; the Windows one shows as the look Windows gives it.</summary>
-    public static ThemeChoice Of(AppTheme theme, Func<bool> windowsUsesLight) => theme switch
+    public static ThemeChoice Of(AppTheme theme) => theme switch
     {
         AppTheme.Light => Light,
         AppTheme.Dark => Dark,
-        _ => windowsUsesLight() ? Light : Dark,
+        _ => Windows,
     };
 
-    /// <summary>Light after dark, dark after light.</summary>
-    public ThemeChoice Other => Theme == AppTheme.Light ? Dark : Light;
+    /// <summary>
+    /// The Windows theme (follows Windows), then the other look, then Windows' look kept fixed, then the Windows theme again:
+    /// the first click always changes the colours.
+    /// </summary>
+    public ThemeChoice Next(Func<bool> windowsUsesLight)
+    {
+        ThemeChoice same = windowsUsesLight() ? Light : Dark;
+        ThemeChoice other = same == Light ? Dark : Light;
+        if (this == Windows) return other;
+        return this == other ? same : Windows;
+    }
 }
 
 internal static class AppThemeExtensions
diff --git a/src/OrthoStreamXP/Gui/MainWindow.xaml b/src/OrthoStreamXP/Gui/MainWindow.xaml
index 8a8d08e..d29c9fc 100644
--- a/src/OrthoStreamXP/Gui/MainWindow.xaml
+++ b/src/OrthoStreamXP/Gui/MainWindow.xaml
@@ -66,10 +66,10 @@
                     </StackPanel>
                 </Button>
 
-                <!-- Theme: the Windows one at first, each click switches between light and dark -->
+                <!-- Theme: Windows (follows Windows), then the other look, then Windows' look kept fixed, then Windows again -->
                 <Button DockPanel.Dock="Bottom" Style="{StaticResource SidebarLink}" Margin="4,0,4,0"
                         Command="{Binding ChangeTheme}" AutomationProperties.Name="{Binding Theme.Label, StringFormat='{}{0} (click to change)'}"
-                        ToolTip="Switch the window between light and dark colours.">
+                        ToolTip="Switch the window's colours: same as Windows, light or dark.">
                     <StackPanel Orientation="Horizontal">
                         <TextBlock Style="{StaticResource Icon}" Text="{Binding Theme.Glyph}" Width="20" />
                         <TextBlock Text="{Binding Theme.Label}" Margin="12,0,0,0" VerticalAlignment="Center" />
diff --git a/src/OrthoStreamXP/Gui/ViewModels/MainViewModel.cs b/src/OrthoStreamXP/Gui/ViewModels/MainViewModel.cs
index 38b65b4..8705524 100644
--- a/src/OrthoStreamXP/Gui/ViewModels/MainViewModel.cs
+++ b/src/OrthoStreamXP/Gui/ViewModels/MainViewModel.cs
@@ -84,7 +84,7 @@ public MainViewModel()
         _selected = Navigation[0];
         HandleProblem = new RelayCommand<ProblemAction>(Handle);
         Donate = new RelayCommand(() => Shell.Open(AboutViewModel.DonationPage));
-        ChangeTheme = new RelayCommand(() => Theme = Theme.Other);
+        ChangeTheme = new RelayCommand(() => Theme = Theme.Next(WindowsTheme.AppsUseLight));
         Mount.PropertyChanged += (_, e) =>
         {
             if (e.PropertyName == nameof(MountController.State)) Raise(nameof(SidebarStatus));
@@ -146,13 +146,13 @@ private set
     /// <summary>Opens the donation page, from the sidebar.</summary>
     public ICommand Donate { get; }
 
-    /// <summary>The sidebar's theme button: switches between light and dark.</summary>
+    /// <summary>The sidebar's theme button: Windows, the other look than Windows', Windows' look kept fixed, back to Windows.</summary>
     public ICommand ChangeTheme { get; }
 
-    /// <summary>The window's look (the Windows one until a click picks one): applied at once and remembered for the next start.</summary>
+    /// <summary>The window's theme (the Windows one follows Windows): applied at once and remembered for the next start.</summary>
     public ThemeChoice Theme
     {
-        get => ThemeChoice.Of(Preferences.Theme, WindowsTheme.AppsUseLight);
+        get => ThemeChoice.Of(Preferences.Theme);
         private set
         {
             if (value.Theme == Preferences.Theme) return;
diff --git a/tests/OrthoStreamXP.Tests/AppThemeTests.cs b/tests/OrthoStreamXP.Tests/AppThemeTests.cs
index 11a90ac..0571497 100644
--- a/tests/OrthoStreamXP.Tests/AppThemeTests.cs
+++ b/tests/OrthoStreamXP.Tests/AppThemeTests.cs
@@ -17,20 +17,26 @@ public void Each_choice_maps_to_its_wpf_theme_mode()
     }
 #pragma warning restore WPF0001
 
-    [Fact]
-    public void A_click_switches_between_light_and_dark()
+    [Theory]
+    [InlineData(true)]
+    [InlineData(false)]
+    public void Clicks_go_windows_then_the_other_look_then_the_windows_look_then_windows(bool windowsUsesLight)
     {
-        Assert.Equal(AppTheme.Dark, ThemeChoice.Light.Other.Theme);
-        Assert.Equal(AppTheme.Light, ThemeChoice.Dark.Other.Theme);
+        AppTheme same = windowsUsesLight ? AppTheme.Light : AppTheme.Dark;
+        AppTheme other = windowsUsesLight ? AppTheme.Dark : AppTheme.Light;
+        ThemeChoice choice = ThemeChoice.Of(AppTheme.System);
+        var seen = new List<AppTheme>();
+        for (int i = 0; i < 4; i++, choice = choice.Next(() => windowsUsesLight)) seen.Add(choice.Theme);
+
+        Assert.Equal([AppTheme.System, other, same, AppTheme.System], seen);
     }
 
     [Fact]
-    public void Until_a_click_the_button_shows_the_look_windows_gives()
+    public void Each_saved_theme_shows_as_its_own_choice()
     {
-        Assert.Same(ThemeChoice.Light, ThemeChoice.Of(AppTheme.System, () => true));
-        Assert.Same(ThemeChoice.Dark, ThemeChoice.Of(AppTheme.System, () => false));
-        Assert.Same(ThemeChoice.Dark, ThemeChoice.Of(AppTheme.Dark, () => true));
-        Assert.Same(ThemeChoice.Light, ThemeChoice.Of(AppTheme.Light, () => false));
+        Assert.Same(ThemeChoice.Windows, ThemeChoice.Of(AppTheme.System));
+        Assert.Same(ThemeChoice.Light, ThemeChoice.Of(AppTheme.Light));
+        Assert.Same(ThemeChoice.Dark, ThemeChoice.Of(AppTheme.Dark));
     }
 
     [Fact]

From 313d2ec625b56c139274588934f4bfa441ae9d78 Mon Sep 17 00:00:00 2001
From: flysimdev <flysimdev@icloud.com>
Date: Tue, 10 Nov 2026 19:26:32 +0100
Subject: [PATCH 4/5] X-Plane skips the mounted package when streaming is
 started from the setup wizard ("Start OrthoStreamXP now") #14

---
 release-notes/v1.2.1.md                       |   3 +
 .../Setup/Installation/DesktopShell.cs        | 130 ++++++++++++++++++
 .../Setup/Installation/SystemCheck.cs         |  13 +-
 3 files changed, 143 insertions(+), 3 deletions(-)
 create mode 100644 release-notes/v1.2.1.md
 create mode 100644 src/OrthoStreamXP/Setup/Installation/DesktopShell.cs

diff --git a/release-notes/v1.2.1.md b/release-notes/v1.2.1.md
new file mode 100644
index 0000000..52c25db
--- /dev/null
+++ b/release-notes/v1.2.1.md
@@ -0,0 +1,3 @@
+## Fixes
+
+- **Photo scenery missing on the first flight after installing.** If you ticked **Launch OrthoStreamXP now** at the end of the installer and then pressed **Start XP**, X-Plane started without the photo scenery and removed the OrthoStream packages from its scenery list. Restarting OrthoStreamXP made it work. **Start XP** now starts X-Plane the same way a double-click in Windows does, so the first flight shows the photo scenery too. Your **X-Plane start options** are still passed to X-Plane as before.
diff --git a/src/OrthoStreamXP/Setup/Installation/DesktopShell.cs b/src/OrthoStreamXP/Setup/Installation/DesktopShell.cs
new file mode 100644
index 0000000..988063b
--- /dev/null
+++ b/src/OrthoStreamXP/Setup/Installation/DesktopShell.cs
@@ -0,0 +1,130 @@
+using System.Runtime.InteropServices;
+using Microsoft.CSharp.RuntimeBinder;
+
+namespace OrthoStreamXP.Setup;
+
+/// <summary>
+/// Starts programs through the desktop's Explorer, as a double-click there would, so they get the person's own
+/// environment instead of inheriting this program's. Started by the installer's "Launch" box, this program's
+/// environment is the installer's, and an X-Plane started from it left the mounted packages out of its scenery.
+/// </summary>
+internal static class DesktopShell
+{
+    private const int CsidlDesktop = 0, SwcDesktop = 8, SwfoNeedDispatch = 1, SvgioBackground = 0, SwShowNormal = 1;
+    private static readonly Guid ShellWindowsClass = new("9BA05972-F6A8-11CF-A442-00A0C90A8F39");
+    private static readonly Guid TopLevelBrowserService = new("4C96BE40-915C-11CF-99D3-00AA004AE837");
+    private static readonly Guid ShellBrowserInterface = typeof(IShellBrowser).GUID;
+    private static readonly Guid DispatchInterface = new("00020400-0000-0000-C000-000000000046");
+
+    /// <summary>
+    /// Asks the desktop's Explorer to start <paramref name="program"/>. Returns false, after logging why, when it could not
+    /// (no Explorer running as the desktop); call this from an STA thread such as the window's.
+    /// </summary>
+    public static bool TryStart(string program, string arguments, string workingDirectory)
+    {
+        var pending = new List<object>();
+        try
+        {
+            object shellWindows = Keep(pending, Activator.CreateInstance(Type.GetTypeFromCLSID(ShellWindowsClass, throwOnError: true)!)!);
+            object location = CsidlDesktop;
+            object? root = null; // an empty VARIANT
+            object? desktop = ((IShellWindows)shellWindows).FindWindowSW(ref location, ref root, SwcDesktop, out _, SwfoNeedDispatch);
+            if (desktop is null)
+            {
+                Log.Warning("The desktop's Explorer is not running; X-Plane is started directly");
+                return false;
+            }
+            Keep(pending, desktop);
+            Guid service = TopLevelBrowserService, shellBrowser = ShellBrowserInterface, dispatch = DispatchInterface;
+            var browser = (IShellBrowser)Keep(pending, ((IServiceProvider)desktop).QueryService(ref service, ref shellBrowser));
+            IShellView view = browser.QueryActiveShellView();
+            Keep(pending, view);
+            // The desktop view's Shell.Application lives in Explorer, so its ShellExecute starts the program from there.
+            dynamic folderView = Keep(pending, view.GetItemObject(SvgioBackground, ref dispatch));
+            dynamic application = Keep(pending, folderView.Application);
+            application.ShellExecute(program, arguments, workingDirectory, "", SwShowNormal);
+            return true;
+        }
+        catch (Exception ex) when (ex is COMException or InvalidCastException or RuntimeBinderException)
+        {
+            Log.Warning($"The desktop's Explorer could not start {program} ({ex.Message}); it is started directly");
+            return false;
+        }
+        finally
+        {
+            foreach (object comObject in pending)
+                if (Marshal.IsComObject(comObject)) Marshal.ReleaseComObject(comObject);
+        }
+    }
+
+    private static object Keep(List<object> pending, object comObject)
+    {
+        pending.Add(comObject);
+        return comObject;
+    }
+
+    // Only the methods used are called; the Slot methods keep the others' places in the interfaces' tables.
+#pragma warning disable CA1707, IDE1006 // the slot names mark unused table entries
+    [ComImport, Guid("85CB6900-4D95-11CF-960C-0080C7F4EE85"), InterfaceType(ComInterfaceType.InterfaceIsDual)]
+    private interface IShellWindows
+    {
+        void Slot_Count();
+        void Slot_Item();
+        void Slot_NewEnum();
+        void Slot_Register();
+        void Slot_RegisterPending();
+        void Slot_Revoke();
+        void Slot_OnNavigate();
+        void Slot_OnActivated();
+
+        [return: MarshalAs(UnmanagedType.IDispatch)]
+        object? FindWindowSW(ref object location, ref object? root, int windowClass, out int window, int options);
+    }
+
+    [ComImport, Guid("6D5140C1-7436-11CE-8034-00AA006009FA"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
+    private interface IServiceProvider
+    {
+        [return: MarshalAs(UnmanagedType.IUnknown)]
+        object QueryService(ref Guid service, ref Guid interfaceId);
+    }
+
+    [ComImport, Guid("000214E2-0000-0000-C000-000000000046"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
+    private interface IShellBrowser
+    {
+        void Slot_GetWindow();
+        void Slot_ContextSensitiveHelp();
+        void Slot_InsertMenusSB();
+        void Slot_SetMenuSB();
+        void Slot_RemoveMenusSB();
+        void Slot_SetStatusTextSB();
+        void Slot_EnableModelessSB();
+        void Slot_TranslateAcceleratorSB();
+        void Slot_BrowseObject();
+        void Slot_GetViewStateStream();
+        void Slot_GetControlWindow();
+        void Slot_SendControlMsg();
+
+        IShellView QueryActiveShellView();
+    }
+
+    [ComImport, Guid("000214E3-0000-0000-C000-000000000046"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
+    private interface IShellView
+    {
+        void Slot_GetWindow();
+        void Slot_ContextSensitiveHelp();
+        void Slot_TranslateAccelerator();
+        void Slot_EnableModeless();
+        void Slot_UIActivate();
+        void Slot_Refresh();
+        void Slot_CreateViewWindow();
+        void Slot_DestroyViewWindow();
+        void Slot_GetCurrentInfo();
+        void Slot_AddPropertySheetPages();
+        void Slot_SaveViewState();
+        void Slot_SelectItem();
+
+        [return: MarshalAs(UnmanagedType.IUnknown)]
+        object GetItemObject(int item, ref Guid interfaceId);
+    }
+#pragma warning restore CA1707, IDE1006
+}
diff --git a/src/OrthoStreamXP/Setup/Installation/SystemCheck.cs b/src/OrthoStreamXP/Setup/Installation/SystemCheck.cs
index 4559b54..bf48d2f 100644
--- a/src/OrthoStreamXP/Setup/Installation/SystemCheck.cs
+++ b/src/OrthoStreamXP/Setup/Installation/SystemCheck.cs
@@ -94,10 +94,17 @@ public static IReadOnlyList<string> TakenInCustomScenery(string? xplane, IEnumer
         return File.Exists(exe) ? exe : null;
     }
 
-    /// <summary>Starts X-Plane from its folder, as a double-click on X-Plane.exe would.</summary>
+    /// <summary>
+    /// Starts X-Plane from its folder, as a double-click on X-Plane.exe would: through the desktop's Explorer, so it does not
+    /// inherit this program's environment (directly only when Explorer cannot).
+    /// </summary>
     /// <param name="arguments">Added to its command line, such as --allow_reshade; null or empty for none.</param>
-    public static void StartXPlane(string program, string? arguments = null) =>
-        Process.Start(new ProcessStartInfo(program, arguments?.Trim() ?? "") { WorkingDirectory = Path.GetDirectoryName(program)!, UseShellExecute = true })?.Dispose();
+    public static void StartXPlane(string program, string? arguments = null)
+    {
+        string folder = Path.GetDirectoryName(program)!, options = arguments?.Trim() ?? "";
+        if (DesktopShell.TryStart(program, options, folder)) return;
+        Process.Start(new ProcessStartInfo(program, options) { WorkingDirectory = folder, UseShellExecute = true })?.Dispose();
+    }
 
     public static bool IsXPlaneRunning()
     {

From 97142f8c7e49f0c4ba46ff196dd6aaf569810850 Mon Sep 17 00:00:00 2001
From: flysimdev <flysimdev@icloud.com>
Date: Tue, 10 Nov 2026 19:49:43 +0100
Subject: [PATCH 5/5] Release notes v1.2.1

---
 release-notes/v1.2.1.md | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/release-notes/v1.2.1.md b/release-notes/v1.2.1.md
index 52c25db..e625b1f 100644
--- a/release-notes/v1.2.1.md
+++ b/release-notes/v1.2.1.md
@@ -1,3 +1,9 @@
+## What's new
+
+- **Light or dark window.** A new theme button at the bottom of the sidebar switches the window between following Windows, always light, and always dark. Your choice is kept for the next start. Thanks to @MarcelL94 for building it (#13).
+
 ## Fixes
 
-- **Photo scenery missing on the first flight after installing.** If you ticked **Launch OrthoStreamXP now** at the end of the installer and then pressed **Start XP**, X-Plane started without the photo scenery and removed the OrthoStream packages from its scenery list. Restarting OrthoStreamXP made it work. **Start XP** now starts X-Plane the same way a double-click in Windows does, so the first flight shows the photo scenery too. Your **X-Plane start options** are still passed to X-Plane as before.
+- **Black text in dark mode.** Some text in the window, such as the sidebar links, the quality preset cards and the on/off switches, showed in black on the dark background and was hard to read. It now uses the theme's text colour in both light and dark mode. Thanks to @MarcelL94 (#13).
+
+- **Photo scenery missing on the first flight after installing.** If you ticked **Launch OrthoStreamXP now** at the end of the installer and then pressed **Start XP**, X-Plane started without the photo scenery and removed the OrthoStream packages from its scenery list. Restarting OrthoStreamXP made it work. **Start XP** now starts X-Plane the same way a double-click in Windows does, so the first flight shows the photo scenery too. Your **X-Plane start options** are still passed to X-Plane as before. Thanks to @MarcelL94 for reporting it (#14).