As many people sit at the wheel of their car, they are certain they know what colour 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.
Author
- Sasha Rakovich
Senior Lecturer in Physics, King's College London
Colour, 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 colour as you do. Colour 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 colour 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 colour. If you've ever picked a paint colour that looked perfect in the shop but turned into something entirely difference once on your walls, you've already encountered this phenomenon.
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This notion of colour 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 colour - 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 colour 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 in varying degrees.
By targeting just the M cones, the scientists at Berkeley have in essence created a pure colour. 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 colour perception.
The most common type of red-green colour blindness, deuteranomaly, occurs when the M and L cones overlap more than they should. This reduces people's ability to distinguish between colours in that range, without affecting sharpness or brightness.
Language may play a role in colour perception , influencing how easily or accurately we discriminate between colours, especially when languages differ in how they categorise or label colour distinctions. This highlights the gulf between an objective property and the processing of the brain.
The difference between the subjective experience of colour 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 minimise reflections. But instead of offering a pure colour, it removes colour altogether - delivering a universal experience of "black" by eliminating visual stimulus.
In truth, artists have known colour 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 colour his work presented to the onlooker by controlling brightness, contrast and the surroundings. Rothko, like the scientists at Berkeley, recognised that colour 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 programme, 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 colour as experience.
The future of colour
Why do so many artists want to patent the blackest black, the bluest blue or the pinkest pink if they know that colour 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 colours like Semple's yolo can create a similar wow feeling.
The work at Berkeley opens the door to a much more direct experience of colour than we've ever had before. Scientists in the future may map the photoreceptors and parts of the brain which process colour, allowing them to beam a range of direct and repeatable experiences into people's brains.
It's important to note that colour 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.
Sasha Rakovich receives funding from the Royal Society (Public Engagement Fund PEFR66002 funds Transcending the Invisible project).
