This seems to have been looked at in aircraft aerodynamics. A Concorde aircraft that was painted blue could not fly as fast as one painted white because of the change in temperature, apparently (although maybe this is because of other thermal related factors):

https://aviation.stackexchange.com/questions/11322/how-big-is-the-influence-of-color-on-the-stability-of-the-boundary-layer

Obviously different colored paints will have different materials in them that could influence smoothness of the surface and resulting aerodynamics, too:

http://www.airliners.net/forum/viewtopic.php?t=771503

Whether this would apply to off-road vehicles traveling at much lower speeds than aircraft like the Concorde, I have no idea.