Impossible colors are colors that can’t appear in ordinary vision. The two main types of impossible colors are forbidden colors and chimerical colors.
Some examples of forbidden colors include reddish green and yellowish blue. These colors aren’t perceivable to the human eye. This is because of how our eyes are made. Cells fire opponent neurons when stimulated by red, green, or blue light. Red and green light cancel each other out. So do blue and yellow light. This is why reddish green and yellowish blue are impossible for us to see. Of course, not everyone believes these colors exist.
In 1983, visual scientists Hewitt Crane and Thomas Plantanida wrote a paper titled “On Seeing Reddish Green and Yellowish Blue”. They used an image similar to the one shown here. They showed it to dozens of volunteers and used an eye tracker to ensure the light from each color stripe always entered the same retinal cells. The volunteers all said they had seen colors they’d never seen before.
But, in 2006, Po-Jang Hsieh and his colleagues conducted a variation of Crane and Plantanida’s experiment. But, this time they gave the volunteers a color map to find the color they say. The experiment showed that the participants saw a mixture of the two colors, not true reddish green or yellowish blue.
Hillock, a National Research Council senior associate at the U/S/ Air Force Research Laboratory, has led several experiments to prove the existence of forbidden colors. According to his research, Hsieh’s experiment used steady eye fixation instead of retinal stabilization. When the striped images are regionally stabilized and equally bright, the perceived color is described as “not muddy at all, but surprisingly vivid”.
Chimerical colors are colors that can’t be seen as a direct response to the colors of light the eye is exposed to. Instead, they are generated in the brain by looking at two colors one after the other. This process induces fatigue in your cones by looking at extremely saturated colors— this temporarily changes their color sensitivities, then looking at a different color.
Three types of chimerical colors include stygian colors (colors that are both saturated and dark), self-luminous colors (colors that appear to glow), and hyperbolic colors (colors that appear more than completely saturated). Some examples of chimerical colors include Stygian blue, self-luminous red, and hyperbolic orange.
Impossible colors are an amazing phenomenon that show just how large the world is. These colors include forbidden colors and chimerical colors. While as humans, we can see around a million different colors, there are still colors that we can’t see.