How We See Color, and Why We Disagree About It

Color seems like the most obvious thing in the world. The sky is blue, the grass is green, and surely everyone sees the same. Then a single photograph of a dress went around the world in 2015 and split humanity into people who saw it as blue and black and people who saw it as white and gold, looking at the very same pixels. That argument was a free public lesson in a deep truth: color is not simply out there in the light. It is built by the brain.

It starts with light

The physical starting point is real. Light of different wavelengths enters the eye, and three types of cone cells in the retina, sensitive to roughly long, medium, and short wavelengths, respond in different proportions. From just three signals the visual system constructs the enormous range of colors we see. People who are color blind usually have a difference in one cone type, which is why the world's color depends on the hardware you happen to have.

But the brain decides

The cones are only the beginning. The brain compares their signals through an opponent process, weighing red against green and blue against yellow, and then performs a remarkable trick called color constancy: it discounts the color of the lighting so that a banana looks yellow at noon and at sunset, even though the light bouncing off it is physically very different. Your brain is constantly guessing the "true" color of a surface by subtracting what it assumes about the light.

The dress

That guessing is what the dress exposed. The photo was ambiguous about its lighting, so brains that assumed cool daylight subtracted blue and saw white and gold, while brains that assumed warm indoor light subtracted gold and saw blue and black. Neither group was wrong about the pixels; they were making different unconscious assumptions about the light. It was a perfect demonstration that perception is inference, the same lesson taught by optical illusions.

Color and language

Even the categories we sort colors into are partly learned. Languages divide the spectrum differently, and some name fewer basic colors than English does, which can subtly affect how quickly speakers distinguish certain shades. Color, then, is a collaboration between physics, biology, and culture, the light, the eye, the brain, and the word, which is why the artist who works with pigment and light is always also working with the mind.