This extension in 8.4+ will produce this in a Lint:
game/defines/outline_shader.rpy:236 In ATL transform 'outline_transform', the 'color' parameter replaces a Ren'Py built-in name, which may cause problems.
This can be fixed by naming it 'color_'
game/defines/outline_shader.rpy:259 In ATL transform 'glow_outline', the 'color' parameter replaces a Ren'Py built-in name, which may cause problems.
game/defines/outline_shader.rpy:266 In ATL transform 'drop_shadow', the 'color' parameter replaces a Ren'Py built-in name, which may cause problems.
If I recall the Github history, they made some changes to built-in name that this may collide with.