.. at the risk of starting a punchup, I have to concur with the earlier post by TES ...
Energy absorption and radiation has to do with electron activity .. that incomprehensible quantum mechanics thing with which we confused ourselves mightily as undergraduates ...
The basic consideration is one of electron mean free paths ... in a material with short distances between atomic level interactions there will be a more effective energy transfer between radiation and lattice energy - both ways. It follows that a material which is a good absorber of EMR will also be a good emitter. In the final analysis, black is both the best absorber and emitter ...
If you are really into brain strain (PPRuNe physicists and mathematicians excluded - and we do actually have a few), dig out a physics textbook and wade through the stuff on blackbody radiation curves. Names like Maxwell, Planck and Wein figure prominently .... as will lots of exponential and quantum equations .... all good fun .. I guess ...