How do humans see color? Eyes detect wavelengths between 380 and 750 nanometers. Below 380 is ultraviolet light, above 750 is infrared. This is possible thanks to cells in our retinas called cones—photoreceptors that respond to specific wavelengths and send signals to the brain, which handles the rest.
- S cones: short wavelengths (blue).
- M cones: medium wavelengths (green).
- L cones: long wavelengths (red).
S, M, and L cones. Cones don’t work in isolation. Their ranges overlap. M cones respond to longer blue wavelengths, and S cones can react to shorter green wavelengths. “There’s no light in the world that can activate only the M cone cells,” Ren Ng, professor of electrical engineering and computer science at the University of California, said. “If they are being activated, for sure one or both other types get activated as well.”
The experiment. That’s the key to the study, published Friday in Science Advances. What if we could stimulate just a few specific cones? That’s exactly what University of California researchers attempted. They mapped the retina, located M cones, and used low doses of laser light to activate them. The technique is called Oz, named after The Wizard of Oz and the Emerald City.
Meet “olo.” After the experiment, participants reported seeing a new color: “olo.” Of the five people involved, three were co-authors of the study, and two were colleagues at the University of Washington. They described “olo” as “an impossibly saturated bluish green.” Ng said the closest way to represent “olo” on a screen is the hex code #00ffcc—only with a level of saturation that’s impossible to grasp because our brains have never processed that signal before.
“The closest way to represent ‘olo’ on a screen is the hex code #00ffcc.”
How do we know it’s real? To confirm that all participants saw a previously unseen color, researchers ran a series of color-matching tests. They compared “olo” to a standard blue-green laser, tweaking saturation by adding white light. Each participant agreed: desaturating “olo” eventually matched the laser’s color, confirming that “olo” lies outside the normal range of human vision.
So, what’s the point? Great question. For now, the discovery doesn’t have a direct practical application—other than proving the process works. But it opens fascinating possibilities. For instance, the lead researchers imagine screens that could scan the retina and display “impossible” colors.
The idea could have more immediate value in areas like helping blind people see specific colors or simulating animal vision through human eyes. The main limitation? The Oz effect is temporary—for now.
Image | Quinten de Graaf (Unsplash)
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