I remember from my 2 cycle racing days that flat black got rid of heat. aluminum paint or polished parts retained it.
Any color paint is more efficient at radiating heat than bare metal. The paint surface has much more surface area than bare metal (but you have too look at it on a microscopic level to see the hills and valleys in the paint). I found a 10 degree C difference on a light fixture that I designed once just by painting it with rattle can enamel.
