When something is painted black, it gains a higher emissivity, and is therefore better at emitting energy. The reason why things appear black rather than white is because they absorb a lot more sunlight than they reflect. They have a low reflectivity. So, things that are painted black both reflect and emit more energy than things that aren't painted black.

Alright, so how come black paint cools down an SR-71 Blackbird more than it heats it up? Is it because it's receiving relatively little energy from relative to the energy it's producing through friction with the air? If I go outside wearing a black shirt in the middle of summer, I'm going to get pretty hot, I'm not going to be get any cooler.