Five Volunteers Witness New Colour Through Laser Experiment
Five volunteers in the United States have become the first people to see a colour that sits outside the normal bounds of human vision after researchers precisely targeted single photoreceptor cells in their eyes with laser light. The new hue, christened “Olo”, was described by participants as an extraordinarily vivid blue-green whose saturation exceeds anything found in nature or on a computer screen.
Pinpointing the retina
The feat relied on “Oz”, an adaptive-optics system that maps every cone cell in a patch of retina and then uses an eye-tracking laser to activate only the medium-wavelength (M) cones responsible for green perception. In normal circumstances, any light energetic enough to excite M cones also stimulates long- or short-wavelength cones, so the brain never receives a pure M-cone signal. By isolating that channel, the Berkeley and Seattle-based team elicited a pattern of neural activity the brain had never processed, leading to the appearance of a brand-new colour.
To keep the tiny beam on target, participants bit down on a stabilising bar while software compensated for involuntary eye tremors. The illuminated field was only a few square millimetres, roughly twice the apparent size of the Moon, but large enough to allow colour-matching tests that confirmed Olo lies outside the established “gamut” of human vision.
A hue beyond all charts
Olo is not merely a brighter teal, the authors stress. When volunteers attempted to match the sensation with monochromatic light, even the most intense 500-nm laser looked dull by comparison. Only by adding white light, thereby reducing saturation, could they coax Olo to converge on an ordinary shade.
External experts caution, however, that Olo cannot be photographed, printed or displayed: it exists solely in the minds of those whose retinas are being actively rewritten.
Why create an impossible colour?
The technology was developed primarily to answer basic questions about how the visual system interprets mixed signals from overlapping cones. But Co-Lead Author Ren Ng believes the same platform could one day simulate missing photoreceptor outputs for people with colour-vision deficiency, giving them temporary access to hues they have never experienced. It could also let scientists model retinal diseases in healthy volunteers by selectively silencing or distorting cone responses.
Despite its promise, Oz is unlikely to appear in consumer electronics soon. The set-up depends on costly adaptive-optics imaging, eye-tracking accurate to one micron and a perfectly still participant; even a blink aborts the trial. Scaling the method to full-field vision, or integrating it into lightweight goggles, would require leaps in miniaturised optics and real-time processing power. For now, Olo remains a laboratory curiosity shared by fewer people than have walked on the Moon.
The Road Ahead
The discovery of Olo pushes the boundaries of neuroscience as much as optics. It shows that colour is not an immutable property of the external world but a construct the brain assembles from cone signals, and that construct can be expanded with the right stimulus. Whether Oz eventually yields clinical therapies or spectacular new art forms, the experiment underscores a central lesson: our perception of reality is only as fixed as the tools we use to probe it.
