I think it would be crazy to do a color change on a car like that, especially for that reason. Exterior color doesn't have that much impact on the inside termperature of the car, not nearly as much as the interior color and the presence or absence of window tint. Color changes are hard - and very expensive to do them right. Take the cheap route and everything looks horrible - door jambs, engine compartment, etc. If you want a light colored car sell it and buy another one.