I believe a nice addition to the game would be an option to change the colour and crominess of the rims.
This would be an awesome feature, and would help cut down on the parts list. Instead of having two seperate wheels (Folk ET73 White and Folk ET73 Black) we could have the one ET73 wheel with a color selector next to it.
You can change the color. You just need to go to the level editor and in the material editor. Then selct "Wheel" and change color. Tutorial: Just don't selct the pickup's material, select the "Wheel"
That method you posted only works on the car's body. I tried to do this for wheels, but it doesn't work. Right now, if you want to change the color of the wheels, you have to change it in the texture file for the wheel.
Hmm..... I think this would be an interesting add-on. But what would be even more fascinating as an option would be the ability to change the 'walls' of a car tire to be different colors without having to re-texture anything and so forth.