Muspuppis, there may be some truth to that: The two fastest man-made objects ever were both made from reflective material. Helios I and Helios II were space probes launched in the 70's to study the sun at close range, and achieved a maximum velocity of 150,000 miles per hour. They appear to have been constructed from some highly polished material, and I can only imagine they would have been at LEAST one or two miles per hour faster if they were green...
*edit* Gasoline, I don't want to make you feel unwelcome to the board, we're just having a little fun. I suspect that there is nothing to be gained or lost by choosing a particular color over another, except as far as weight is concerned. A car with absolutely no paint at all would be lighter, and therefore slightly faster, assuming all else to be equal. I doubt that any standard formulation of wheel paint would significantly affect brake performance either, otherwise a quick glance at what they're doing to f-1 cars should tell you what color to paint both your car, and your wheels.