How many colors can we make

Why we can see colors

For the majority of people, colors are a natural part of their daily life. But why can we see colors at all, and how does that work? Dogs, cats or bulls cannot do it, and obviously still find their way around the world quite well. The fact that we can recognize and differentiate colors gives us a whole range of advantages that make the survival of our evolutionary ancestors in the wild, but also our orientation in modern civilization, considerably easier and safer. The act of seeing color itself, and the fact why we can determine with certainty what color an object is, is a rather laborious process.

The color is not created in the eye, it is in the brain

First of all, it has to be stated that our eyes are not outstanding from a physical and visual point of view. The image of our surroundings that is projected onto the retina is not of particularly good quality: it is spatially and color-distorted, quite blurred and is also upside down. Only the brain reconstructs from the information of the eyes with the help of biochemical processes and with the inclusion of other stored information a picture of our environment, as we are used to it and in which we can move safely. Incidentally, this also means that the colored image that we perceive is created with the help of our stored knowledge, our experience, our interests and, last but not least, our personal mood and state of mind. This also makes it clear why two people see the same thing at the same moment, but are very likely to perceive it differently.

Cones and chopsticks

In addition to the pure projection onto the retina, our eyes provide even more information that is crucial for the creation of a colored image. Electromagnetic radiation, in the form of light of different wavelengths, hits our eyes and penetrates the cornea, iris, pupil, lens and vitreous body until it hits the retina. On the side of the retina facing away from the light there are two different types of so-called photoreceptors. That is around 120 million so-called rods and around 6 million cones. The rods are very light-sensitive and responsible for light / dark vision, whereas the less light-sensitive cones are responsible for color vision.

The brain as a color mixer

Three different types of cones (L, M, and S) each absorb a specific wavelength range of light. The so-called "long cones" perceive the area that our brain then interprets as red, while the medium or short cones register the proportion of green and blue. They owe their specific sensitivity for the respective spectral range to certain pigments, which change their molecular structure when exposed to light. They trigger signals that the sensory cell forwards in the form of an impulse to a ganglion cell in the nervous system. This receives the signals of the different types of cones and calculates them against each other. From this information with the respective proportions of the three basic color information, our brain can determine the exact mixture and thus the correct color tone. Our brain, on the other hand, needs the information from the rods in order to recognize spatial depth and contrasts by means of the black and white components of the light. Since they are very sensitive to light, they enable us to orientate ourselves even in low light. When it is dark, they do most of the work and the cones are no longer active. That's why we don't see colors in the dark.

Different colors due to different light

The key requirement for being able to see colors is light. And in our eyes, the objects get their color by the objects either absorbing or reflecting light of different wavelengths. Basically, the color impression arises from the property of the surface of an object to reflect certain parts of the light more strongly than others. For example, water appears blue to us because the red, yellow and green parts of sunlight are absorbed very quickly and the blue part is reflected most strongly. If the color or wavelength of the light is changed, for example by means of filters, the color of the illuminated object also changes. A red apple suddenly appears black in the green light.

A goldfish sees more

The human eye can perceive light with wavelengths between 380 nm and 780 nm (nanometers). This is only a small part of the entire electromagnetic radiation spectrum. We cannot see 60 percent of the wavelengths contained in sunlight, such as UV light. In this regard, many birds are superior to us, some of which have four color receptors. Even a goldfish has a wider spectrum of color vision than humans. The way in which the eye and brain process this enormous amount of information at any given moment so that we can see has not yet been fully clarified.