People really see different colors

Do all people perceive colors in the same way?

In February 2015, a snapshot of a dress sparked lively discussions on the Internet. What color was it? Some were sure: blue-black! Rather, the others thought they saw a white gold fabric. It is now clear that ambiguous lighting and personal visual experiences led to these different impressions. But one question remained open: do we actually see the same thing as our fellow human beings when we look at a colored object?

The human eye is able to distinguish up to 2.3 million color tones. This is made possible by visual cells that react to light of different wavelengths. We can only see light in a very specific spectrum: from 400 to 700 nanometers. In the short-wave range it appears blue to violet to us, long-wave light we see red. Most color impressions result from a mixture of different wavelengths.

This article is included in Spectrum Compact, keep your eyes open! - How we see the world

Humans have two types of photoreceptor cells: rods, which we use at dusk, and cones, which are responsible for vision in daylight. Rods do not react to certain wavelengths because they are all constructed in the same way. That is why we cannot see colors in the dark. People with normal color vision have three different types of cones, each responding to short, medium, and longer wavelengths. If those cones that are sensitive to shorter wavelengths are more excited than the others, then we perceive the color blue. The cones themselves are color-blind, so to speak. Rather, neurons in the retina convey the color impression by comparing and calculating the excitation states of the different types of cones.

The human eye is able to distinguish up to 2.3 million color tones

How many cones are on the retina and how sensitive they are to certain wavelengths can vary from person to person. However, the signal that is passed on to the brain by the color-sensitive neurons after the calculation is no longer very different. That is why we perceive colors much more similarly than the differences in the number of cones suggest.

Why is that? According to one theory, the neurons in the retina must gradually adapt to the information from the cones. In the first months of life, despite different input signals, they always pass on the same output signal to the brain. Newborn babies are therefore not yet able to correctly recognize colors. A child also has to learn what the colors are called - and the boundaries between green and blue can differ depending on the language and culture.

So people perceive colors very similarly. An exception are people with color ametropia such as red-green weakness. Affected people either have fewer than three types of cones or their cones respond to different wavelengths. Color vision problems are often genetically caused, but can also arise in the course of life.