This Impossible New Color Is So Rare That Only Five People Have Seen It

Researchers discover a new color outside the range of human color vision, but you have to laser your retinas to see it

Rock quartz texture, nature pattern

Teal is as close as you can get to seeing the new color without having your eyes lasered.

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The average human eye can see as many as 10 million variations in color, according to some estimates, from purest gray to laser green. Now scientists say they’ve broken out of that familiar range and into a new world of color. In a paper published in Science Advances, researchers detail how they used a precise laser setup to stimulate the retinas of five participants, making them the first humans to see an impossibly saturated bluish-green beyond our visual range.

Our retinas contain three types of light-detecting photoreceptors, or cone cells. S cones pick up relatively short wavelengths, which we see as blue. M cones react to medium wavelengths, which we see as green. And L cones are triggered by long wavelengths, which we see as red. These red, green and blue signals travel to the brain, where they’re combined into the full-color vision we experience.

But these three cone types handle overlapping ranges of light: the light that activates M cones will also activate either S cones or L cones. “There’s no light in the world that can activate only the M cone cells because if they are being activated, for sure one or both other types get activated as well,” says Ren Ng, a professor of electrical engineering and computer science at the University of California, Berkeley. Ng and his research team wanted to get around that fundamental limitation, so they developed a technicolor technique they call Oz.


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“The name comes from The Wizard of Oz, where there’s a journey to the Emerald City, where things look the most dazzling green you’ve ever seen,” Ng explains. On their own expedition, the researchers used lasers to precisely deliver tiny doses of light to select cone cells in the human eye. First they mapped a part of the retina to identify each cone cell as an S, M or L cone. Then, using the laser, they delivered light only to M cone cells.

It wasn’t exactly a comfortable setup. “This is not a consumer-oriented device, right? This was a basic visual science and neuroscience project,” Ng says. In fact, the researchers experimented on themselves: three of the five participants were co-authors of the paper. The two others were colleagues from the University of Washington who were unaware of the study’s purpose.

As one of the participants, Ng entered a darkened laboratory and sat at a table. “There were lasers, mirrors, deformable mirrors, modulators, light detectors,” he says. Next he had to bite down hard on a bar to keep his head and eyes still. As the laser shone on his retina, he perceived a tiny square of light, roughly the size of a thumbnail viewed at arm’s length. In that square, he glimpsed the Emerald City: a color the researchers have named olo.

An illustration uses a digital color swatch to describe an approximation of the color olo.

Ripley Cleghorn

What, exactly, does olo look like? Ng describes it as “blue-green with unprecedented saturation”—a perception his brain conjured up in response to a signal it had never before received from the eye. The closest thing to olo that can be displayed on a computer screen is a version of teal: the color represented by the hexadecimal code #00ffcc, Ng says. (This hexadecimal code is also sometimes referred to as sea green, aquamarine and bright turquoise.) If you want to try envisioning olo, take that color as the starting point and imagine that you are adjusting it on a computer. You keep the hue itself steady but gradually increase the saturation. At some point, you reach the limit of what your screen can show you, but you keep increasing the saturation past what you can find in the natural world until you reach the limit of saturation perceptible by humans, resulting in what you’d see from a laser pointer that emitted almost exclusively teal light. Olo lies beyond even that range.

To find out whether what the participants saw as olo really was a color beyond humans’ standard visual capabilities, the researchers conducted color-matching experiments in which participants could compare olo with a teal laser and adjust the color’s saturation by adding or subtracting white light. All participants found that if they added white light to olo, desaturating it, the new color matched the laser, confirming that olo lies beyond the normal human range of color vision.

“It’s a fascinating study, a truly groundbreaking advance in the ability to understand the photoreceptor mechanisms underlying color vision. The technical demands necessary to achieve this are enormous,” says Manuel Spitschan, who studies light’s effects on human behavior at the Max Planck Institute for Biological Cybernetics in Tübingen, Germany, and the Technical University of Munich and was not involved in the new study. “An open question is how this advance can be used.”

Ng’s team dreams of one day building screens that can scan your retina to display perfect images and videos by delivering light to individual cones—enabling crisp, nonpixelated visuals in impossible colors. “That’s going to be extremely hard to do, but I don’t think it’s out of the realm of possibility,” Ng says. More immediately, he speculates, Oz could be used to let congenitally color-blind people experience colors such as green and red for the first time—although it wouldn’t be an actual treatment for the condition. “The Oz experience is transient,” Ng says. “It’s not permanent.”

“It’s a technical breakthrough, and I would love to have it in my lab,” says Maarten Kamermans, who studies vision and the retina at the Netherlands Institute for Neuroscience and was not involved in the new study. “Think of animal research. We could impose animal types of photoreceptors on human subjects to say, ‘Oh, this is really what a dog would see, what a mouse would see, what a goldfish would see,’” he says. “Now this would be interesting.”

Jacek Krywko is a freelance writer who covers space exploration, artificial intelligence, computer science and all sorts of engineering wizardry.

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Scientific American Magazine Vol 333 Issue 1This article was originally published with the title “Impossible Teal” in Scientific American Magazine Vol. 333 No. 1 (), p. 12
doi:10.1038/scientificamerican072025-4xIwtiLIyaPHMFO6D5dzMj