This simplified view clearly shows that the blue dot on the top of the cube and the one on the darker side are exactly the same hue, reflecting light with identical intensity, or luminance.

Beau Lotto's lab has created dozens of optical illusions to study the systematic goofs that evolution has built into our minds. He proposes that visual glitches are the result of a brain that is beautifully calibrated to detect biologically relevant information--responding effectively to motion (which might indicate a predator on the run) while messing up on simple color matching, which generally has little relevance to survival.