Scientists have achieved what was previously thought impossible by creating a new colour that exists beyond the normal range of human vision.
The groundbreaking discovery, published today in Science Advances, saw researchers use precision laser technology to enable five participants to perceive an extraordinarily saturated bluish-green hue they've named "olo".
The breakthrough came from a team at the University of California, Berkeley, who developed a technique to stimulate specific cone cells in the human retina.
By targeting only the M cone cells responsible for detecting green wavelengths, they bypassed the natural limitations of human colour perception that have confined us to viewing fewer than 10 million colours.
The colour closest resembles a light teal
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Human vision relies on three types of cone cells in the retina, each detecting different wavelengths of light.
S cones respond to short wavelengths perceived as blue, M cones to medium wavelengths seen as green, and L cones to long wavelengths appearing as red. These signals combine in the brain to create our full-colour experience. However, a fundamental limitation exists.
Ren Ng, a professor of electrical engineering and computer science at UC Berkeley, explained: "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."
This overlap between cone responses has historically restricted the range of colours humans can perceive.
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The Emerald City was the inspiration behind the technique
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The team named their technique "Oz" after the Wizard of Oz's Emerald City. "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.
The experimental setup was far from comfortable. Participants entered a darkened laboratory filled with "lasers, mirrors, deformable mirrors, modulators, light detectors," according to Ng, who was among the test subjects alongside two other study co-authors.
Each participant had to bite down on a bar to keep their head completely still whilst lasers mapped their retinal cone cells.
The precision laser then delivered light exclusively to M cone cells, creating a thumbnail-sized square of unprecedented colour in their vision.
The colour is closest to #00ffcc
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Ng describes olo as "blue-green with unprecedented saturation" - a perception the brain created in response to signals it had never before received.
The closest approximation on a computer screen would be teal, specifically the hexadecimal code #00ffcc, though olo extends far beyond any displayable colour.
Verification experiments confirmed participants were seeing beyond normal human vision. When white light was added to desaturate olo, it matched a standard teal laser.
"It's a fascinating study, a truly groundbreaking advance in the ability to understand the photoreceptor mechanisms underlying colour vision," Manuel Spitschan from the Max Planck Institute for Biological Cybernetics said.
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