Hi, this is a cool idea. Would it be possible to also implement country flags like https://mods.factorio.com/mod/train-trails does, or even allow custom input of color pattern? (for example - comma delimited list of colors like FF0000,00FF00,0000FF in string setting)

The custom colors mod option already allows for exactly that so good news for you i suppose lol
There is one country already in as a sort of joke but probably gonna delete it in the next update. Theres a lot of countries which would quickly cause menu bloat, and specifying colors from country flags shouldn't be too hard since most have 3 colors.

Ah, nice, very cool then!