I've been facing this problem from a long time, Whenever I use /svc (in apartments) it only changes the main color and the other one becomes black, that's in some vehicles which have 2 colors, Adding this would help people alotBut, if you'll keep the current one the way it is now, it'd be better so people don't need to open a GUI to add a color they already know.
You obviously don't know how to use /svc, please next time check the usage of it and then post.The usage of /svc is: Command usage: /setvehcolor r g b (r g b must be 0 to 255) r2 g2 b2 (optional) meaning you can change the first and second color of the vehicle. However I don't really see the usage of this update, nowadays /svc is barely used by players, even I knew about it just recently. If you want your RGB color just get it from /headlightsI think this will be a waste of time for the developers.