Will painting an in-home heating radiator the color black positively/negatively affect its heat output?”
Paint an object black might help if it was receiving sun-based heat, because little of the light would be reflected. If your radiator was in bright sunlight, then it might be useful, because any sunlight would be absorbed and there would be les energy used in heating up the radiator later. Of course, in the summer, the radiator would heat up due to the sunlight and affect air conditioning/ You could drape it with a white sheet in the summer.
