In our world, cars have been historically sold in many different palettes. For example, a 50s American fullsize would have different colours, all with a different look, than a modern compact sedan. So why isn't that the case in Beam? Why don't we have more color/segment-appropriate ranges, just like any other aspect of the cars?
Well currently paint options are quite limited anyways, you can't quite have a proper metallic or candy paint. Even just gloss and matte paint aren't perfect, so untill paint system gets reworked, I think it is just better to let it be the way it is.