Well why do black, I even would think I wish also in white. The vision of the human eye does not seem to see only "visible light" of the electromagnetic wave and thus where the light from the light source does not reach (shadow) is "visible light" is not reflected (or the amount is small) it is for. Why shadow or black (darkness), I its human vision is it from the (also said that cannot be recognized, what color) recognize as "black". By the way, if there is a heat differences in the darkness, and you will be recognized If you look at where the "thermography" as the heat distribution of the "infrared".