This Japanese manga girl by professor Akiyoshi Kitaoka looks like she has one cyan eye and one gray eye. In fact, both eyes are exactly the same shade of gray. The proof can be seen right next to the original. The girl’s right eye appears the same as the turquoise hair clip, only because of the reddish context. Scientific American explains this optical illusion in following words: “Part of the process of seeing color is that three different kinds of photoreceptors in the eye are tuned to three overlapping families of color: red, green and blue (which are activated by visible light of long, medium and short wavelengths). These signals are then instantaneously compared with signals from nearby regions in the same scene. As the signals are passed along to higher and higher processing centers in the brain, they continue to be compared with larger and larger swaths of the surrounding scene. This “opponent process,” as scientists call it, means that color and brightness are always relative.”
