A color known as olo has drawn renewed attention after an experiment used precisely targeted light to activate medium-wavelength cone cells in the retina while largely avoiding the other cone types. The resulting experience cannot be reproduced by an ordinary screen, printed sample or single wavelength of visible light.
Human color vision normally involves overlapping responses from S, M and L cone cells. No monochromatic stimulus activates only the M cones because their sensitivity overlaps with the other two classes. Researchers worked around that limitation by mapping part of each participant's retina, identifying individual cones and delivering small laser doses through adaptive optics and scanning laser ophthalmoscopy.
Five participants in the University of California, Berkeley experiment officially experienced olo. They described it as a blue-green with an intensity beyond colors encountered in ordinary viewing. Co-author Ren Ng characterized it as more saturated than a real-world color. The nearest representation within the sRGB gamut is identified as hexadecimal `#00FFCC`, but that patch is only an approximation and is not olo itself.
The color was reported on April 18, 2025. Its name derives from theoretical coordinates of 0, 1 and 0 in LMS color space, corresponding to isolated M-cone stimulation and spelling olo in a leet-style reading. The experimental square covered an angular width of 0.9 degrees, roughly twice the apparent diameter of the Moon.
Researchers have explored whether the underlying method might eventually help enhance color perception for people with color-vision deficiencies. Ng has also raised the possibility of a form of expanded vision resembling tetrachromacy. Those ideas remain prospective applications rather than demonstrated treatments in the described experiment.
The claim that olo is a genuinely new color is disputed. Some specialists regard the precise stimulation method as a major technical accomplishment while questioning whether the subjective result should be classified as a new color. John Barbur of City St George's, University of London, said that interpretation remained open to argument.
That debate separates two issues. The experiment created a retinal activation pattern that normal illumination cannot produce, and its participants reported an unusually saturated percept. Whether that percept expands the category of human colors is a question of definition as well as technique. For everyone outside the five-person study, digital samples can indicate the hue family but cannot reproduce the actual visual experience.
The renewed interest also led artists to ask about paints inspired by olo. Such pigments can imitate the reported blue-green direction, but they remain constrained by ordinary illumination and the overlapping response of retinal cones; they cannot recreate selective cellular stimulation.
