Ok, another thing you could do is make it two different models that always stay in the same position but delete the faces of the parts that aren't part of the logo (the main body) and then have the other model just be the the main body (so you separated the original model into two, one with the parts that do change color and one where they don't). Then always keep the models at the same position and just change the color of the car body so you can keep the logo the same color.