i don't think the color of the paint would make any diff in temp...sure a white shirt is cooler than black in the sun, but i don't think that works for engines, altho i have been told that chrome holds heat in...so no more chrome oilpans for me...
i do know that on some race engines they paint inside of water jackets w/ same kinda paint they paint inside of electric motors, that supossed to help heat transfer to the water, forgot its name, but i've seen them pour it in and turn engine all around to paint inside...its a thermal type coating...its in electric motors for same reason, to help transfer of temp to the housing and fins...dielectric paint....thats what it's called..just came to me...