We really are splitting poofteenths here,intercoolers as you say use convection,but anything painted a dark colour will absorb and retain more heat from outside sources than if the same item where painted a light colour.The thicker the paint colour is added will not effect temperature,six coats of black paint will carry the same temp.as one coat over a measured time.

This is all a bit hard is'nt it? Shiny is good i reckon

(we did paint chemistry in the old days at trade school)