Can you imagine a reddish green? Not the muddy brown produced by mixing red and green paint, but a gloriously vivid color that looks a bit like red and a bit like green. How about a color that looks like a mix of blue and yellow, yet isn’t greenish? These exist, but are virtually impossible to see or envision — except with the help of retinal stabilization. Someday we may wear goggles to see the forbidden colors previously off limits. Via Life’s Little Mysteries:
“The observers of this unusual visual stimulus reported seeing the borders between the stripes gradually disappear, and the colors seem to flood into each other. Amazingly, the image seemed to override their eyes’ opponency mechanism, and they said they perceived colors they’d never seen before.”
Even though those colors exist, you’ve probably never seen them. Red-green and yellow-blue are the so-called “forbidden colors.” Composed of pairs of hues whose light frequencies automatically cancel each other out in the human eye, they’re supposed to be impossible to see simultaneously. Scientists are finding out that these colors can be seen — you just need to know how to look for them.
The color revolution started in 1983, when a startling paper by Hewitt Crane, a leading visual scientist, and his colleague Thomas Piantanida appeared in the journal Science. Titled “On Seeing Reddish Green and Yellowish Blue,” it argued that forbidden colors can be perceived. The researchers had created images in which red and green stripes (and, in separate images, blue and yellow stripes) ran adjacent to each other. They showed the images to dozens of volunteers, using an eye tracker to hold the images fixed relative to the viewers’ eyes. This ensured that light from each color stripe always entered the same retinal cells; for example, some cells always received yellow light, while other cells simultaneously received only blue light.
Wherever in the image of red and green stripes the observers looked, the color they saw was “simultaneously red and green,” Crane and Piantanida wrote in their paper. Furthermore, “some observers indicated that although they were aware that what they were viewing was a color (that is, the field was not achromatic), they were unable to name or describe the color. It seemed that forbidden colors were realizable — and glorious to behold!
You may never experience such a color in nature, or on the color wheel — a schematic diagram designed to accomodate the colors we normally perceive — but perhaps, someday, someone will invent a handheld forbidden color viewer with a built-in eye tracker. And when you peek in, it will be like seeing purple for the first time.