so in connection to the black body discussion, as i remember right what i learnt about radiation n stuff, the color black is black because it absorbs all the light it gets and convert it to heat.
For example, if you see a red car, that is because the material is absorbing all the light from the sun and only reflecting red thus you see red. So if there’s a possibility that you can direct a light bean that doesn’t have any red in it, the car would be black to out eyes.
So with that, black absorbs everything and heat itself up. That is why we use those reflective shinny folding thingys to cover glass in the car, coz it reflects almost all the light including Infrared.
When talking about radiators (water or oil) the purpose is to remove the heat from the liquids and release that to the air. So heat conducts from oil to the metal tubes n fins through convection thus not having anything in-between the two is better. The primary way of releasing heat from the radiator’s outer surface to the air is by convection. Thus according to what i know, having nothing in-between is the best as well. But to reduce corrosion n stuff a coating is applied that has the maximum coefficient of conductivity. Color really doesn’t matter in that sense.
But lastly we have to give consideration to the environment the cooler or the radiator is in, it gets sunlight, and heat radiated from the engine. So with that the main method that heat will be transmitted to the radiator is through radiation. Thus, according to what i understand its better to have a outer appearance in light shinny color (i.e, aluminium) so that it won’t absorb the IR from the environment.