A team of researchers has just generated the perception of a new color they’ve dubbed “olo,” which apparently has never been seen before. The lucky winners were five people whose photoreceptors were stimulated with a laser.

First of all, it’s important to clarify that colors don’t “exist” as such, since what we perceive in the retina, at the back of the eye, is light. There, our photoreceptors (the cones) transform it into nerve impulses, and these, once processed, are interpreted by our brain as color. This is equivalent to what we know as the visible spectrum , a very narrow portion of the electromagnetic spectrum.

Specifically, the wavelengths of light responsible for our perception of colors interact with the cones. It’s the combination of that information, depending on which cones are stimulated, that allows our brain to resolve the color (or colors) we’re seeing.

A matter of cones

Humans are trichromats because we have three types of cones : those that respond to longer wavelengths (L), which we perceive as red; those that respond to medium wavelengths (M), which we perceive as green; and those that respond to shorter wavelengths (S), which we perceive as blue. In other words, we see in RGB ( red, green, blue).

This graph shows how the stimulation band of the M cones overlaps with those of the S and L cones. Wikimedia Commons

In total, we have 6 million cones, and color perception depends on how and how many are activated at any given time. Each object absorbs a series of wavelengths and reflects others, which correspond to the color we are seeing. Thanks to all this, humans can distinguish around a million colors. And none of them are the ones that have just been discovered.

The researchers asked themselves what a person would perceive if only one type of cone were activated. To do this, they used a device they called the Oz Vision System (named after the Emerald City in L. Frank Baum’s novel The Wizard of Oz ), a laser capable of selecting and stimulating around 1,000 photoreceptors of a single modality in isolation, without involving the other two types.

Using this system, the scientists stimulated only the M cones (those that respond to wavelengths we perceive as green) in a small area of ​​the eye in the five participants in the experiment. They reported seeing a blue-green color more intense than any they had ever perceived before.

A unique experiment

The green cones span the middle of the visible spectrum, so their stimulation range overlaps with that of the red (L) and blue (S) cones. In the case of the latter two, there are certain “natural” conditions in which some wavelengths can stimulate them in isolation, but because of this overlap with the L and S cones, independent activation of the M cones is not possible under typical lighting conditions.

Therefore, using this type of laser, which can independently isolate and stimulate M photoreceptors, was the only way to test whether it is possible to generate colors that do not exist in normal human perception.

The name of the new color is associated with the terminology used in binary coding, the combinations of 0 and 1 used to represent data in computing. “OLO” represents the binary number 010: of the three cone types, since only the M type is activated, it is represented as 0 (the S type is not stimulated), 1 (the M type is stimulated), and 0 (the L type is not stimulated).

How can someone know if they have never seen a color before?

The subjects described “olo” as a “blue-green with unprecedented saturation.” However, color perception has both objective (color deficits, visual problems, etc.) and subjective components. A person can infer whether what they are seeing is novel or not by comparing it with previous experiences, for example, but this assessment is subjective.

To verify that all participants actually perceived a color completely different from their familiar ones, color matching experiments were conducted, comparing their perception of “olo” with that of a blue-green laser beam, the saturation of which was adjusted by adding white light. All five participants agreed that, when white light was added to “olo”—that is, reducing its saturation—the result matched the color of the laser. This confirmed that “olo” is outside the visible spectrum known to humans.

In any case, from an objective and scientific perspective, a person cannot know with absolute certainty whether a color they are perceiving has never been seen before, since there is always a subjective component that is difficult to overcome.

Furthermore, we can’t be 100% sure that anyone on this planet, due to some anomaly in their cones, has the ability to perceive “olor” naturally, even if they’re not aware of it. Or how can we be certain that a tetrachromat , capable of identifying up to 100 million shades in our visible spectrum, can’t distinguish “olor” without the need for microlaser pulses? It’s something difficult to prove.

Can we play “olo” so everyone can see it?

It’s impossible to see “olo” with the naked eye. By its nature, it cannot be reproduced either physically or digitally. There is no “natural” light stimulation that exclusively activates the M cones of our retina. Although we may already find images circulating that claim to resemble a highly saturated blue-green color, that wavelength they represent cannot activate only our M cones.

As for the potential practical applications of Oz Vision, this tool could be invaluable in basic research to explore still-unknown functions of our photoreceptors, as it allows specific groups of these cells to be isolated and studied in conscious individuals, something that was previously impossible.

Furthermore, it could help us better understand the mechanisms that lead to visual diseases in which photoreceptors are damaged or lost, opening up new avenues for preventing or treating them.

The authors also suggest that generating the perception of novel colors in experiments with human subjects could have future applications in the creation of new, enriched, and personalized experiences, in vision therapy, or even in communication and art. Although promising, these applications still seem far from reality.

Author Bio: Conchi Lillo is Professor at the Faculty of Biology, researcher of visual pathologies at the University of Salamanca