on a new map - the default first selected tile is none

[blurymind]

on a new map - the default first selected tile is none.
This leads to being able to paint the map with red squares, until you select a tile

[BellBlitzKing]

Found source. It's "ctx.fillStyle = red" , which fills in a color when texture not yet found / loaded or active tile unasigned/null.

Link: @blurymind

tilemap-editor/src/tilemap-editor.js

Line 609 in 758cdbb

ctx.fillStyle = 'red';

Solution 1:
Make that starting color to "transparent" so "ctx.fillStyle = transparent"
When a user is first start clicking around, it's just empty blocks, so it's obvious they need to select a tile first.

Solution 2:
Make the starting color the same color as a full single-color tile in your tileset.
For example, in the demo tileset, there is a white all-color tile and a tan all-color tile. Maybe pick the color on those.
So when the app first loads & a user is clicking around, it Appears as though a tile is preselected from among the tileset, so it will not be interpreted as an error in any way.