Hi! I am not quite sure if this is a valid question, but I'll give it a shot. What my education managed to teach me about how materials emit or reflect colors is, that it's (usually) related to electrons changing their energy levels. Though there are other causes like bremsstrahlung. Thus I was wondering, assumed it would be possible to do in any way, if there is a way of telling what a nugget of some elementary particle would look like. Say, if you could overcome the repulsive forces, and create a macroscopic ball of electrons. Or protons, some quark, or any other particle that is not an atom (or nucleus). I know that this is probably highly unlikely to be actually accomplished, but it would be nice if there was a way to tell this from some theory. Would such a material emit light? Reflect? What frequency? Or would such a thing just be black and dark on any level, even if bombarded with EM radiation? Maybe fully transparent? Thanks in advance for any insight!