Actually its colors in the "white" (white light is made of all colors) end of the spectrum that reflect light the most. Black and dark colors absorb light, thats why the look dark, where as bright colors reflect more light to your eye making them look bright. So if everything inside the headlights were black, you'd end up with a 100W headlights that seem to have to output of a flashlight.
Light has energy which we feel as heat (sunlight), a light or white colored car will be significantly cooler than a dark or black car sitting in the smae parking lot under a summer sun because most of the light and heat energy was reflected (light car) vs. absorbed (dark car).
This is my understanding...if I'm wrong..then please correct me so that I can go and change my major.
CCC