... So what it is about is the difference in our perception from what is actually given. Or to put it another way: The question of what conclusions the surface allows for the structure hidden beneath it. This is what the Greek term "chroia" means: its meaning changes between "color" or "surface". These terms mark the boundary by means of which the bodies distinguish themselves from one another and from their surroundings: They only allow limited conclusions to be drawn about the internal structure of these bodies. It also sets limits to our capacity for knowledge, insofar as it is dependent on sensual perception.

(Ingo Dorfmüller)