What are colours and how do people understand them? | Explained Premium

The role of colour in human experience, perception, and culture explored through science, history, and art.

Colour plays an outsized role in the human experience of modern life. It invests both natural and synthetic worlds with beauty and meaning. Colours don’t deny universalism — a red sign will make you stop anywhere on the planet — yet they also make room for human cultures to appropriate them in unique, even discordant, ways. As the human understanding of colour has improved, and continues to do so, this knowledge has also broadened our sense of our place in this world, and the other life-forms with which we share it.

Colour is a type of information our eyes receive and process based on electromagnetic radiation. An object by itself can’t be said to have a colour — but based on which frequencies of visible-light radiation it absorbs, reflects, and/or scatters, we can perceive the object to have a particular colour.

In the human eye, the rod and the cone cells receive information in the light that strikes the eye: the rod cells record brightness while the cone cells record the wavelengths, which the human brain interprets as colour. Human beings have three types of cone cells. Each type is sensitive to light of a different wavelength, and they work together to input colour information to the brain.

The possession of three types of cone cells is why humans are called trichromats. Many birds and reptiles, on the other hand, are tetrachromats (four types of cone cells). Similarly, while human vision is restricted to wavelengths from 400 nm to 700 nm (a.k.a. visible light), honeybees can also ‘see’ ultraviolet light and mosquitoes and some beetles can access information in some wavelengths of infrared radiation. (Humans sense the latter has heat.)

This limitation, such as it is, is why those spectacular images captured by space telescopes of celestial wonders like nebulae need to be false-coloured: to highlight the information secreted in radio waves, X-rays, gamma rays, ultraviolet light, etc. Seen in visible light alone, many of these images will have much less visual detail.

There are many ways to produce specific colours. The art of mixing some colours to produce others is rooted in colour theory.

Until the late 19th century, traditional colour theory specified the different ways in which dyes, pigments, and inks could be mixed to make other colours. In this paradigm, there were three primary colours — e.g. red, yellow, and blue — that when combined in different ways could produce all the colours the human eye is capable of seeing.