Depending on trial conditions, the human brain-eye (breye) can distinguish about 100 shades of gray (at about 1% increments from the ‘0’ of black to the ‘100’ of white). Similarly, or perhaps not at all similarly, the human breye can discern over 10 million unique colors.
We submit here that, all things being equal, information delineated through contrast has greater comprehensible density than comparable data expressed though tone.