A truly new color would be impossible to describe, for the same reason you can’t describe red to someone who has never seen it. Your brain builds every color you’ve ever experienced from just three types of signals, and a new color would require a signal that doesn’t exist in your visual system. That said, scientists have found several ways to push the boundaries of human color perception, and the results offer the closest glimpse we have of what “new” might look like.
Why Your Brain Can Only Mix Three Ingredients
Human color vision starts with three types of cone cells in the retina, each sensitive to a different range of light wavelengths: roughly red, green, and blue. Every color you’ve ever seen is your brain’s interpretation of the ratio of signals from those three cone types. Purple, for instance, isn’t a single wavelength of light. It’s your brain’s response to red and blue cones firing simultaneously while green cones stay relatively quiet.
This three-channel system also creates hard limits. Your visual processing treats red and green as opposites on the same channel, and blue and yellow as opposites on another. A signal can slide toward red or toward green, but it can’t go both directions at once. That’s why you can imagine a reddish blue (purple) or a yellowish red (orange), but “reddish green” doesn’t produce any mental image at all. The wiring simply doesn’t allow it. A genuinely new color would need to exist outside this three-dimensional mixing space entirely, like a direction that isn’t up, down, left, right, forward, or back.
Forbidden Colors That Shouldn’t Exist
Reddish green and bluish yellow are sometimes called “forbidden colors” because the opponent-channel system blocks them. But researchers have managed to force the brain to see them anyway, using a clever trick. Vincent Billock and his colleagues created images of adjacent red and green stripes (and separately, blue and yellow stripes), then used an eye tracker to lock the image perfectly in place on the retina. Normally your eyes make tiny movements that keep the visual system refreshed. When the image is stabilized, something strange happens: the borders between stripes dissolve, and the two opponent colors flood into each other.
Observers reported seeing colors they had never encountered before. Billock described the experience as “like seeing purple for the first time and calling it bluish red.” The colors were vivid, not muddy. When the experiment was done improperly, with one stripe brighter than the other, people saw unremarkable olive or brownish mixtures. But when the stripes were equally bright and properly stabilized, the result was genuinely novel. This suggests the brain can be coaxed past its own rules under the right conditions, producing a color experience that has no name and no match anywhere in ordinary vision.
Chimerical Colors and Afterimage Tricks
You can experience a milder version of “impossible” color at home through afterimages. Stare at a saturated color for 30 seconds or more until the cone cells responsible for it become fatigued, then shift your gaze. The exhausted cones underrespond, and the remaining cones dominate, creating an afterimage in the complementary color. This much is ordinary. But the specific conditions of fatigue can produce colors that sit outside the normal range of experience.
These are called chimerical colors, and they come in a few varieties. Stygian colors appear simultaneously as dark as black and as saturated as a vivid hue, something that doesn’t happen in normal vision (dark colors are always desaturated). Self-luminous colors appear to glow as if lit from within, even though you’re looking at a plain white surface. Hyperbolic colors appear more saturated than any physically possible color, like a green so intense it exceeds what green light can actually produce on your retina. Each of these represents the brain generating a color signal that no real-world light source could create.
What Animals See That You Can’t
If you want to imagine what an entirely new dimension of color might look like, the animal kingdom offers some perspective on just how much is out there beyond human perception. Mantis shrimp have 12 types of color receptors compared to our three, and they can detect ultraviolet and polarized light. They don’t simply see “more colors” the way adding more crayons to a box gives you more shades. They sample light in ways that are structurally different from anything the human brain processes.
Arctic reindeer have evolved the ability to see ultraviolet light, which is abundant in the snow-covered Arctic environment. UV reflects differently off vegetation and different types of snow, so what looks like a uniform white landscape to a human eye is full of contrast and detail to a reindeer. Their world contains visual information that is simply invisible to us. It isn’t that UV “looks like” a very deep purple. To an animal with dedicated UV receptors, it’s processed as its own channel, as distinct from violet as red is from blue.
This is the core problem with imagining a new color. Asking what ultraviolet looks like to a reindeer is like asking what sound looks like. The information arrives through a channel your brain doesn’t have. You can translate it into a channel you do have (the way a thermal camera maps infrared to visible colors), but the translation is a workaround, not the real thing.
People With a Fourth Cone Type
A small number of humans may actually see more colors than the rest of us. Tetrachromacy, the condition of having four types of cone cells rather than three, is genetically possible in women who carry certain variants of the genes for red and green receptors. Estimates of potential tetrachromats among Caucasian women range from 15% to 47%, depending on which genetic variants are counted.
Having the extra cone type is necessary but not sufficient. Most potential tetrachromats don’t seem to use the fourth channel in a meaningful way. But in testing, some women with the right genetics perceive more distinct colors in diffracted light spectra than people with standard three-cone vision. Researchers have speculated that functional tetrachromats experience a dimension of color that trichromats are simply denied. For them, two paint swatches that look identical to everyone else might be clearly, obviously different, distinguished by a quality no three-cone viewer can access or name.
Technology as a New Sense
Neil Harbisson, an artist born completely color-blind, has worn a head-mounted sensor since 2004 that converts light wavelengths into vibrations on his skull, which he perceives as sound. Over time, his brain adapted to interpret these signals as a form of color experience. He later upgraded the sensor to include infrared and ultraviolet wavelengths, extending his perception beyond what even typical human vision covers. He’s described walking through a forest and sensing which plants have high UV reflectance because they register as loud and high-pitched.
Harbisson’s experience points to something important: the brain is flexible enough to build new perceptual categories from unfamiliar input. He doesn’t “see” infrared the way a pit viper does. He hears it. But his brain has assigned it a distinct sensory quality that lets him navigate the world using information the rest of us ignore entirely. This is probably the closest any human has come to perceiving a genuinely new color, even though the pathway is auditory rather than visual.
The Philosophical Wall
Philosopher Frank Jackson captured the fundamental difficulty with a thought experiment in 1982. Imagine a scientist named Mary who has spent her entire life in a black-and-white room. She has studied every physical fact about color vision: how wavelengths stimulate the retina, how signals propagate through the brain, which neural patterns correspond to the word “red.” She knows everything there is to know about color in scientific terms. The question is: when Mary steps outside and sees red for the first time, does she learn something new?
Most people’s intuition says yes. There’s something about the experience of red that can’t be captured by any description of wavelengths and neural firing patterns. That irreducible “what it’s like” quality is what philosophers call qualia. And it’s exactly why no article, no metaphor, and no amount of explanation can tell you what a new color would look like. The experience of seeing a color is fundamentally different from knowing facts about it.
So the honest answer is: a new color would look like nothing you can currently imagine, because imagining it requires the very neural machinery you don’t have. The forbidden-color experiments and chimerical afterimages are the nearest anyone has come to genuinely novel color experience within normal human biology. They suggest the brain can go beyond its usual limits when forced, producing percepts that are vivid, real, and nameless. But a truly new primary color, as different from red, green, and blue as they are from each other, would require a new type of sensor in the eye and new wiring in the brain to interpret it. Until then, it remains the one thing you can’t picture.