black or brass
First of all, yes, black does help dissipate heat. That's why back in the early '70s the 'cool' thing to do was paint your aluminum intake black to help dissipate engine heat and cool the intake charge. Some people did, but I just kept mine aluminum as it just looked so much better.
I also stripped the paint from the upper tank on my old '69 340 Swinger and polished the brass. Popped the hood and it really looked good with the polished brass radiator, polished aluminum valve covers, natural-finish aluminum intake and white-painted headers (remember, it was the early '70s). I always kept everything spotless under the hood. I had more than a couple of buddies cuss me whenever they would toss a shop rag on the inner fender and they'd immediately slide down and under the headers because the inner fenders were waxed and shined just like the rest of the outside body did.
My 'new' '69 Dart is gonna be the same unless I decide to go with an aluminum radiator.
Another reason for the paint on the brass tanks is to keep the brass finish from corroding.
