Credit: Pixabay/CC0 Public Domain

As many people sit at the wheel of their car, they are certain they know what color is. It's the red traffic light in front of them, the garish yellow hatchback in the next lane, or the green verge banking to their right.

Color, as many people understand it, is the property of a thing. That light is green. The sky is blue. But scientifically, that's not quite true. No one can experience the exact same color as you do. Color is a perceptual experience created by our brains.

It's the interaction between a material, light and the mind. The way a material absorbs and scatters light affects what reaches our eyes. And color needs to be processed by the brain.

The shape of objects and the context in which you encounter them can also shape the way you perceive color. If you've ever picked a paint color that looked perfect in the shop but turned into something entirely different once on your walls, you've already encountered this phenomenon.

This notion of color as experience was recently shown in a study by researchers at the University of California, Berkeley, who used lasers to manipulate participants' eyes into seeing a new color—a blue-green they call olo.

To achieve this, the scientists used lasers to activate specific photoreceptor cells in the retina that detect green wavelengths of light, called M cones. We also have S and L cones, types of photoreceptors that detect short blue, and longer red wavelengths of light respectively. Everyone has slight variations in the number and sensitivity of these cones, so we each experience color a little differently.

Outside the lab, the reflected light that comes into our eyes illuminates large areas of the retina, which stimulates multiple cone types. The wavelengths perceived by the M and L cones overlap by over 85%. This means that under natural conditions, the two are always activated together, but to varying degrees.

By targeting just the M cones, the scientists at Berkeley have in essence created a pure color. Olo doesn't have context or material conditions. It will look the same to different people.

But this isn't the only example which shows the place of the brain in color perception.

The most common type of red-green color blindness, deuteranomaly, occurs when the M and L cones overlap more than they should. This reduces people's ability to distinguish between colors in that range, without affecting sharpness or brightness.

Language may play a role in color perception, influencing how easily or accurately we discriminate between colors, especially when languages differ in how they categorize or label color distinctions. This highlights the gulf between an objective property and the processing of the brain.

The difference between the subjective experience of color and the fixed, physical means of producing it means that most artists' search for "pure" paint will fail. British artist Stuart Semple recently claimed he'd recreated olo in paint form. He called the paint yolo. But when people look at it, M and L cones will be activated at the same time. A "pure" paint is still impossible.

Semple's Black 3.0, along with other ultra-black materials, is marketed as a "pure" black paint. It absorbs nearly all light, using a high concentration of light-absorbing pigments and a matte binder to minimize reflections. But instead of offering a pure color, it removes color altogether—delivering a universal experience of "black" by eliminating visual stimuli.

In truth, artists have known color is a matter of perception for quite some time. The modernist artist Mark Rothko was notoriously meticulous about how his work was displayed. Rothko insisted that his work be hung low, with as little white wall visible as possible, in dim light.

He was shaping the experience of color his work presented to the onlooker by controlling brightness, contrast and the surroundings. Rothko, like the scientists at Berkeley, recognized that color is an interaction between material, light and observer. It is not just about manipulating what we don't see, but about engineering what we do.

I have been running a public engagement program, Transcending the Invisible, which brings together scientists and artists to explore scientific ideas through art. What I've been struck by most is that scientists and artists share this understanding of color as experience.

The future of color

Why do so many artists want to patent the blackest black, the bluest blue or the pinkest pink if they know that color can't be made "pure" with pigment?

Berkeley researcher Austin Roorda described having a "wow" experience at perceiving something entirely new when he saw olo.

We need to accept that colors like Semple's yolo can create a similar wow feeling.

The work at Berkeley opens the door to a much more direct experience of color than we've ever had before. Scientists in the future may map the photoreceptors and parts of the brain which process color, allowing them to beam a range of direct and repeatable experiences into people's brains.

It's important to note that color isn't just sensory data but something that shapes how we feel, remember and connect to the world. Artists like Rothko, Van Gogh and Kandinsky had an innate understanding of that which scientists are only now starting to piece together.

This article is republished from The Conversation under a Creative Commons license. Read the original article.