Depending on your disciplines, black could be the appearance of a substance that absorbs all spectrums of light and reflects none, as in the pigments of a painter's pallet, lamp, bone, char or ink. Or it could be what you see when deep within a cave, the total absence of light. Either way, black is full of poetic resonances, it's meaning shifting like a chameleon, to signal according to its context.
So what is black to you?