It sounds like something from science fiction, but a team of scientists in the United States has made a rather bold claim: they believe they have experienced a colour previously unseen by human eyes. After hundreds of thousands of years on Earth, you might think we’ve seen every shade possible under the sun. This research suggests perhaps not.

The assertion, which hasn't gone unchallenged, comes after an unusual experiment involving researchers having laser pulses directed carefully into their own eyes. The idea was that by precisely stimulating individual light-sensitive cells in the retina – the layer at the back of the eye – they could push human colour perception beyond its usual boundaries. This group of scientists, primarily from the University of California, Berkeley, and the University of Washington, believe they succeeded.

Understanding the colour Olo

So, what is this supposedly new colour like? The researchers involved, numbering five participants in the initial study published in Science Advances, describe it as a type of blue-green. However, they stress that this simple description doesn't do justice to the actual experience. They've coined the name Olo Colour for this perception.

Ren Ng, an electrical engineer at UC Berkeley and one of the study's co-authors who experienced the colour, described it vividly. "We predicted from the beginning that it would look like an unprecedented colour signal but we didn’t know what the brain would do with it," he said. "It was jaw-dropping. It’s incredibly saturated."

To offer some point of reference, the research team shared an image of a turquoise square, stating it was the closest approximation they could create using conventional display technology. But they insist the actual experience of Olo is far more intense. Austin Roorda, a vision scientist also on the team, emphasised this point: "There is no way to convey that colour in an article or on a monitor... The colour we see [on a screen] is a version of it, but it absolutely pales by comparison with the experience of Olo."

Prof Ng offered an analogy to explain the difference in saturation: "Let's say you go around your whole life and you see only pink, baby pink, a pastel pink. And then one day you go to the office and someone's wearing a shirt, and it's the most intense baby pink you've ever seen, and they say it's a new colour and we call it red." In essence, Olo is claimed to be a saturated blue green shade, but with an intensity beyond anything achievable through natural light or current technology.

How researchers saw this colour

The process of perceiving the Olo Colour wasn't straightforward; it involved a sophisticated experimental setup and direct laser stimulated colour perception. It relied on targeting specific cells within the retina.

Our ability to see colour comes down to specialised cells in the retina called cone cells. Most humans have three types of cone cells, each primarily sensitive to different wavelengths of light: * L-cones: Most sensitive to long wavelengths (perceived generally as reds). * M-cones: Most sensitive to medium wavelengths (perceived generally as greens). * S-cones: Most sensitive to short wavelengths (perceived generally as blues).

Our brain interprets the varying levels of stimulation across these three cone types to produce the rich tapestry of colours we see in the world. Natural light, whether from the sun or artificial sources, is always a mixture of different wavelengths. This means that when we look at something, multiple cone types are usually stimulated simultaneously to varying degrees. For instance, looking at something yellow stimulates both L-cones and M-cones significantly. Looking at cyan stimulates M-cones and S-cones.

Critically, the researchers noted that M-cones (medium wavelength, green-sensitive) have sensitivities that overlap significantly with both L-cones and S-cones. Because of this overlap, under normal circumstances, it's thought to be impossible for natural light to stimulate only the M-cones without also triggering the L or S cones to some extent.

The Berkeley team aimed to bypass this natural limitation. Their experiment used a specialised device, previously developed by some team members and updated for this study, nicknamed 'Oz vision' (a nod to the Emerald City). The process involved several steps: 1. Mapping the Retina: First, they meticulously mapped a small area of a participant's retina to identify the exact locations of individual M-cone cells. This requires high-precision imaging techniques. 2. Targeted Laser Pulses: A sophisticated system involving mirrors, lasers, and optics then directed a very fine laser beam into the participant's pupil. 3. Selective Stimulation: Using the map, the system targeted individual M-cones. Crucially, the system had to account for the natural tiny movements of the eye (microsaccades) in real-time. When the laser was perfectly aligned with a targeted M-cone, it fired a brief pulse of light specifically calibrated to stimulate that cell. 4. Scanning: The laser then moved on to the next identified M-cone in the mapped area, repeating the process.

The five participants (four male, one female, all with normal colour vision, including three co-authors of the paper) looked into the Oz device during the procedure. The cumulative effect of stimulating many M-cones in near isolation across the targeted patch resulted in the perception of a distinct patch of colour in their field of vision, reportedly about twice the apparent size of the full moon. This perception was the Olo Colour.

Why scientists call Olo a 'new' colour

The core of the claim that Olo Colour represents a new colour discovered rests on the highly artificial way it was generated. As mentioned, natural light invariably stimulates a combination of cone types due to overlapping sensitivities. Red light predominantly activates L-cones, blue light mainly activates S-cones, but M-cones are always stimulated alongside others.

The experiment, through laser stimulated colour techniques, aimed to achieve what natural light cannot: near-exclusive M cone stimulation. By firing laser pulses precisely at M-cones while largely avoiding neighbouring L and S cones, the researchers believe they sent a signal pattern from the retina to the brain that simply doesn't occur in everyday life.

The name 'olo' itself reflects this specific stimulation pattern. It derives from the binary sequence '010'. This signifies: * 0: L-cones (red-sensitive) are not significantly stimulated. * 1: M-cones (green-sensitive) are significantly stimulated. * 0: S-cones (blue-sensitive) are not significantly stimulated.

Therefore, the researchers argue, the resulting perception isn't just a variation of green or blue-green that we already know; it's the brain's interpretation of a novel input signal, one that falls outside the gamut of colours produced by natural light mixing. It pushes perception beyond its normal operating range by isolating one specific colour channel in a way nature doesn’t allow.

Expert perspectives on the discovery

As might be expected with such a striking claim, the idea that Olo Colour is truly a new colour discovered is contested within the vision science community. Not everyone agrees with the interpretation presented by the Berkeley and Washington researchers.

One prominent sceptic is Professor John Barbur, a vision scientist at City St George’s, University of London, who was not involved in the study. While acknowledging the technical achievement of selectively stimulating cone cells ("a technological feat"), he questions the conclusion that this constitutes a 'new' colour.

Professor Barbur suggests that what the participants likely experienced is not fundamentally new, but rather an extremely saturated blue green – specifically, a highly saturated green. He stated, "It is not a new colour. It’s a more saturated green that can only be produced in a subject with normal red-green chromatic mechanism when the only input comes from M cones."

His perspective implies that isolating the M-cone signal doesn't create a new colour category but pushes an existing one (green/blue-green) to an intensity level not normally reachable. He compared it to stimulating only red cones intensely, which would likely be perceived as a very deep, saturated red, perhaps brighter or different in quality depending on sensitivity, but still fundamentally red. From this viewpoint, the work, while technically impressive, might have "limited value" in terms of discovering genuinely novel colour experiences.

This debate highlights a fundamental question in colour science: is colour defined purely by the physical stimulus (wavelengths of light) or by the resulting neural signals and subjective perception? The Olo experiment generates a neural signal pattern potentially never before created naturally, leading the study authors to call the perception new. Critics argue that if the perception falls within an established category (like blue-green), even if hyper-saturated, it's not truly 'new'. The existence of the Olo Colour as something genuinely novel is therefore "open to argument," depending on one's definition.

What this research could mean

Regardless of whether Olo Colour is classified as truly 'new' or an ultra-saturated existing hue, the underlying technology and findings hold potential significance for vision science. The researchers themselves view the work primarily as basic science, a tool to explore fundamental questions about how our brains construct visual perception from the signals received from the eyes.

The ability to selectively stimulate specific cone cell types offers a unique way to probe the visual system. Potential areas of application and further research include:

• Understanding Colour Vision: By isolating inputs from different cone types (or combinations thereof), scientists could gain deeper insights into how these signals are processed and integrated in the brain to create our perception of the full colour spectrum. It allows for testing the visual pathway with highly controlled, unnatural stimuli.
• Colour Blindness Research: Colour blindness (colour vision deficiency) often results from issues with one or more types of cone cells. The Oz vision technology could potentially be adapted to study these conditions more precisely. For example, researchers might investigate how individuals with different forms of colour blindness respond to targeted stimulation of their functioning cones, potentially leading to better understanding or even diagnostic tools. Prof Ng specifically mentioned the team is looking into what the findings could mean for colour blind people.
• Studying Eye Diseases: Certain diseases, like retinitis pigmentosa or macular degeneration, damage photoreceptor cells (cones and rods) in the retina. The ability to map and attempt to stimulate remaining healthy cells selectively could offer insights into disease progression and potentially inform future therapeutic strategies aimed at restoring or augmenting vision.
• Probing Neural Processing: The brain's interpretation of the '010' signal as 'olo' provides data on how the visual cortex handles novel or extreme inputs. It helps researchers understand the limits and flexibility of our perceptual systems.

While the immediate focus is on foundational research, the development of tools like Oz vision represents an advancement in our ability to interact directly with the cellular machinery of sight.

Is Olo Colour something you can see?

Based on the researchers' descriptions, the experience of Olo Colour sounds intriguing. But can the average person expect to see it? The short answer is no, not through any normal means.

The researchers are very clear on this point: Olo Colour is an artifact of their specific experimental setup involving laser stimulated colour perception via the Oz vision device. * Not in Nature: It cannot be produced by any natural light source because sunlight and typical artificial lights always contain a mix of wavelengths that stimulate multiple cone types. The unique condition of near-exclusive M cone stimulation doesn't happen naturally. * Not on Screens: Current display technologies (smartphones, TVs, computer monitors) cannot replicate Olo. These screens work by mixing red, green, and blue light (RGB), similar to how our eyes mix signals from L, M, and S cones, but they operate within the bounds of what natural light combinations can produce. They cannot achieve the selective M-cone-only stimulation required. The turquoise square the researchers shared is merely the closest approximation within the limits of standard screen technology. * Beyond VR: Even advanced virtual reality headsets are nowhere near capable of replicating the effect. VR stimulates vision by presenting images on small screens close to the eyes, still bound by the principles of RGB colour mixing. The technology required involves precisely mapping and stimulating individual retinal cells with lasers, which is far beyond current consumer electronics.

So, for the foreseeable future, experiencing the Olo Colour remains limited to participants in highly specialised laboratory experiments using equipment like the Oz vision system. It's not a colour you'll find in a paint swatch or see on your television.

Looking ahead

The claim by scientists that a new colour discovered through laser stimulated colour techniques has certainly captured attention. The Olo Colour, described as an incredibly saturated blue green, is said to arise from achieving near-exclusive M cone stimulation, a feat impossible under natural lighting conditions.

While the assertion that it represents a fundamentally 'new' colour remains contested by some experts, who argue it may be an extreme saturation of an existing hue, the research undeniably pushes the boundaries of experimental vision science. The techniques developed offer a novel way to investigate the intricate relationship between photoreceptor cells, neural signals, and our subjective perception of colour.

The potential uses of the Olo Colour research lie primarily in advancing our fundamental understanding of vision, with possible future implications for studying conditions like colour blindness and retinal diseases. However, the researchers emphasise that this is basic science. As Ren Ng stated, "We’re not going to see Olo on any smartphone displays or any TVs any time soon." It remains a fascinating glimpse into the possibilities that arise when technology allows us to interact with our biology in highly specific ways, revealing hidden potentials within our own senses.