Multiple texture used to change the same object? no need to. Special settings will change the main body texture using the same texture.
In game it'll change from default to many other colors like this.
Lead artist testing my cars asset in game. The other two cars in this scene also done by me.
Another test in Edge (Eagle Dynamic Graphic Engine).
Neat topology is good, but to me most important is see how the smoothness of a model react on light in game. Really important.