I know that on our circle track motors the block, heads & top of intake are all painted black & the underside of the intake is painted white. I know that it's an old shool trick, but black does dicipate heat better than other colors & also makes my $10000 motor look like crap & people don't really wonder what's in it. Also the white is supposed to conduct heat the least out of all colors. I remember reading something that said that a polished surface dicipates heat the worst, I also remember seeing something on Horsepower TV a few months ago about this also.
In reality I can't see it making any really difference on our cars (well street cars), but in racing (especially cirlce track) where you're beating on somthing much harder & longer & need consistancy then I can see it being something to consider.