What does red look like to you? Philosophers have argued about this for centuries. Maybe my red is your green. Maybe we live in private color worlds, forever unknowable to anyone else.
A new study suggests otherwise. Neuroscientists Michael Bannert and Andreas Bartels at the University of Tübingen found that people’s brains respond to colors in remarkably consistent ways. Using brain scans and clever machine learning tricks, they showed that you can predict the color someone is seeing by comparing their brain activity to that of others.
“We can’t say that one person’s red looks the same as another person’s red,” Bannert explained in a press release. “But to see that some sensory aspects of a subjective experience are conserved across people’s brains is new.”
Cracking the Neural Rainbow
The researchers recruited 15 volunteers with normal color vision. While the participants lay inside an fMRI scanner, they looked at shifting rings of color: red, green, or yellow, each shown at different brightness levels. The team also mapped each person’s retinotopy (the layout of how their visual cortex corresponds to the visual field) using flickering black-and-white checkerboards.
This second step was key. By aligning people’s brains based on shared patterns of spatial processing, Bannert and Bartels could look for hidden commonalities in how brains respond to color. They then trained a linear classifier (a type of machine learning algorithm) on the brain data from some participants. They tested whether it could predict which colors other participants were seeing.
And it worked. In fact, color and brightness could be decoded across different brains with high accuracy in multiple regions of the visual cortex, including V1, V2, V3, hV4, and LO1. “We predicted what color someone is seeing based on their brain activity,” the authors wrote, “using only knowledge of color responses from other observers’ brains.”
Andreas Bartels put it more simply when speaking with Nature: “Now we know that when you see red or green or whatever colour, that it activates your brain very similarly to my brain.”
The Evolutionary Code Behind Shared Shades
This isn’t just about brain-reading party tricks. The study revealed large-scale “retinotopic color biases”. In other words, certain brain regions consistently leaned toward representing specific colors in specific parts of the visual field. Those biases were area-specific, yet conserved across individuals.
That suggests some kind of deep functional or evolutionary logic. As the authors put it, these area-specific spatial color codes “suggest functional or evolutionary organization pressures that remain to be elucidated.”
Jenny Bosten, a color-vision scientist at the University of Sussex, who wasn’t involved in the work, said she was surprised. The idea that some brain cells are biased toward particular colors “doesn’t really fit with our theory of how those areas of visual cortex process colour.” Still, she acknowledged, if the finding holds up, “it might change how we view colour-coding in the cortex.”
Color has always been slippery to pin down scientifically. Sure, you can define it precisely as a wavelength of light. Red light has longer waves, with wavelengths around 620 to 750 nm, while green light falls within the range of approximately 495 to 570 nm. However, the trouble lies in how our brains interpret these wavelengths bouncing off objects. That’s why colors can look different under changing light, or why illusions like “the dress” went viral for splitting the internet into blue-black versus white-gold factions.
So, Do We See the Same Colors?
This new research doesn’t end the philosophical debate about qualia — whether my red feels the same as your red. But it does ground color experience in something more universal: shared brain patterns.
So, next time you’re watching a sunset with a friend, know that your brains are likely humming along in sync. The crimson streaks lighting up the sky are also lighting up the same neighborhoods of your visual cortex.
We may never climb inside each other’s heads to compare the raw feeling of color. But thanks to neuroscience, we now know that beneath the surface, our minds are painting with a surprisingly common palette.
The findings appeared in the Journal of Neuroscience.
