[azraelswrd]

I suspect there's not much difference at conventional road speeds for cars. When I look at a NASCAR track and see the entire spectrum of colors on everything -- makes me think that since they're not all just a few colors, there is probably no edge to just a few colors.

But in theory darker colors should absorb more energy, translate that into heat, transferring part of that energy back to the air and decreasing the air density... sounds pretty small though.