This is an interesting thread. I would have to agree with 69MOPE. I can not see how a different pigment in the paint would affect heat dissipation from the inside. If you took two identical radiators in a controlled environment, temperature, humidity, ventilation and NO light, induced heat into each, it would be logical that the pigment in the black paint would not make the heat dissipate any faster. Now in the real world a black radiator may seem to dissipate heat more only because it would absorb more heat from the surrounding environment and have more to dissipate. Where a light colored radiator would not absorb energy from its surrounding environment and would not have to dissipate this extra heat to start with.