History of Forbidden Colours

Click on the image to enlarge. Cover one segment, and stare intently at the division within the red-green or the blue-yellow segment until the boundary between the two colours disappears. Image Source: Life's Little Mysteries.

I have some posts pointing to online histories of different colours (see here for Haint Blue, and here for Red). Life's Little Mysteries has recently discussed the history of two colours outside the range of human vision. In the 1983, Hewitt Crane and Thomas Piantanida published a paper in Science, entitled, "On Seeing Reddish Green and Yellowish Blue."  They argued that an optical illusion allows us to perceive colours that exist beyond the physical capabilities of our retinas (Hat tip: Free Will Astrology).

The two colours are red-green (not a brown mixture, but a colour that is both red and green at the same time) and yellow-blue (again, a colour that is both yellow and blue simultaneously). These colours do not have names because they are not usually perceived. Having successfully seen the red-green colour in the chart above, the word I would use to describe it is 'Apple.' The blue-yellow was more difficult, but I caught sight of something I would call, a 'Sunlit Sky.'

Chromoscape 116-Yellow Blue Sky © by Beki Borman.

Shutterstock Stock Photo, Yellow Meadow under a Blue Sky with Clouds © Andrey Tiyk.

Seeing these colours is somewhat analagous to one focus of this blog, namely, how the invisible intangibilities of virtual reality are brought to bear on real life. By means of a simple illusion, one's mind allows one to see what one normally cannot physically see. We do something beyond ourselves; it is a little act, which pushes back the boundaries of perception and ability. The photos above show approximations of these colours, and let us know that they do indeed exist. But until this test was devised, their true tones existed outside our ken.

The results of this experiment reflect a 'third-eye' problem common with many Millennial ideas, mysteries and riddles, especially in the west. At the turn of the Millennium, there are all sorts of attempts, conscious or not, to overcome Cartesian dualism. Whether through technical ghost-hunting, or through particle collider searches for the God Particle or Dark Matter there is a strange Millennial literal-mindedness to these experiments. While the Postmodernism of the 20th century assumed that the third configuration was undefinable and unattainable, Millennial Post-Postmodernism adamantly and yet casually insists that we can and will get there. Life's Little Mysteries:

[E]ven though th[e]se 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.

The limitation results from the way we perceive color in the first place. Cells in the retina called "opponent neurons" fire when stimulated by incoming red light, and this flurry of activity tells the brain we're looking at something red. Those same opponent neurons are inhibited by green light, and the absence of activity tells the brain we're seeing green. Similarly, yellow light excites another set of opponent neurons, but blue light damps them. While most colors induce a mixture of effects in both sets of neurons, which our brains can decode to identify the component parts, red light exactly cancels the effect of green light (and yellow exactly cancels blue), so we can never perceive those colors coming from the same place. ...  

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. ...  

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.

See all Colour Histories.