Only Five People Have Seen This New Impossible Color

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

By Jacek Krywko edited by Allison Parshall

There are only so many colors that the typical human eye can see; estimates put the number just below 10 million. But now, for the first time, scientists say they’ve broken out of that familiar spectrum and into a new world of color. In a paper published on Friday 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 a color beyond our visual range: an impossibly saturated bluish green.

Our retinas contain three types of cone cells, photoreceptors that detect the wavelengths of light. 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.

On supporting science journalism

If you’re enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.

Ng and his research team wanted to try getting around that fundamental limitation, so they developed a technicolor technique they call “Oz.”

“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 portion of the retina to identify each cone cell as either 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 study. The two others were colleagues from the University of Washington, who were unaware of the purpose of the research.

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

What, exactly, did olo look like? Ng describes it as “blue-green with unprecedented saturation”—a perception the human 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 teal, or the color represented by the hexadecimal code #00ffcc, Ng says. If you want to try envisioning olo, take that teal as the starting point: Imagine that you are adjusting the latter on a computer. You keep the hue itself steady but gradually increase the saturation. At some point, you reach a limit of what your screen can show you. 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 entirely teal light. Olo lies even further than that.

To check if what the participants saw as olo really was a color beyond humans’ standard visual range, the researchers completed color-matching experiments in which they 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 would match 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 patients experience colors such as green and red for the first time—but this wouldn’t be an actual treatment. “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”.