Home made fan shroud.

RichB said
They call it a radiator because it RADIATES heat. There is a big difference in the amount of radiation based on color and temperature difference. Paint conducts heat and then radiates it from its surface depending on its color. If air is hotter than the surface, a black color then absorbs the heat while a white color reflects more heat.

So what you are saying is that in a pitch black environment, where color has no effect on anything, something painted black will radiate heat more than something painted white.
I think you are think of surfaces radiating heat from the sun, not surfaces radiating heat from within.