Color vision

Color vision is a special ability that helps us see the world in different colors. It is part of how we see and understand light around us. When light enters our eyes, special cells called photoreceptors react to different types of light. These reactions then travel through a network of cells in our brain, allowing us to tell the difference between colors and brightness.

Colorless, green, and red photographic filters as imaged by camera

Many animals, not just humans, have color vision. This ability evolved over time to help animals find food, like ripe fruit or colorful flowers, and to notice important things in their environment. In primates, which include monkeys and apes, color vision likely developed to help them survive by seeing details that might otherwise be hidden.

Wavelength

Isaac Newton found that when white light is split into its colors using a dispersive prism, it can be changed back into white light with another prism.

The visible light spectrum is the range of light humans can see, from about 380 to 740 nanometers. Colors like red, orange, yellow, green, cyan, blue, and violet are found in this range. Light with wavelengths longer or shorter than this is called infrared or ultraviolet, which humans cannot see, but some animals can.

When the wavelength of light changes enough, we see a different hue. In very dim light, our eyes use special cells called rod cells to see, but these do not help us see color. In brighter light, like daylight, other cells called cone cells help us see color. Mixing different colors or using just a few can make us see "white" light.

Dimensionality

Color vision is organized based on how many main colors, or primaries, are needed to show all the colors we see. This number is linked to special proteins called photopsins in our eyes. Most animals with a backbone, like us, originally had four of these proteins, allowing them to see many colors. But some animals have lost one or more of these proteins, so they see fewer colors. The number of colors an animal can see ranges from just one up to four.

Dimension	Characteristic	Occurrence
Achromacy	lack of any color perception	Most skates
Monochromacy	1D color vision	Some mammals, including Pinnipeds, Cetaceans and Xenarthra
Dichromacy	2D color vision	Most mammals and a quarter of color blind humans
Trichromacy	3D color vision	Most Old World monkeys and apes, including most humans; possibly monotremes and some marsupials
Tetrachromacy	4D color vision	Most birds, reptiles and fish, and rarely in humans
Pentachromacy and higher	5D+ color vision	Rare in vertebrates

Physiology of color perception

Seeing color starts with special cells in your eyes called cone cells. These cells have special proteins that help them sense different colors of light. Humans have three types of cone cells, which help us see a wide range of colors.

Color vision is a complex process that begins in the eye and continues in the brain. While some cells in the eye sense basic colors, the brain combines this information to create the full experience of color that we see. This process involves many steps and different parts of the brain working together.

The same figures as above represented here as a single curve in three (normalized cone response) dimensions

Cone type	Name	Range	Peak wavelength
S	β	400–500 nm	420–440 nm
M	γ	450–630 nm	534–555 nm
L	ρ	500–700 nm	564–580 nm

Subjectivity of color perception

Further information: Color appearance

Color is something we see and feel, and it changes based on what we see. Most people think we all see colors the same way, but some thinkers have wondered if that’s true. For example, someone might see what we call “red” as a different color than we do. This idea has never been proven in real life.

Some people can even see colors when they hear sounds or think of shapes, which shows how personal our experience of color can be. Different groups of people, like the Himba people, see and name colors in ways that are unique to their lives.

Chromatic adaptation

Main article: Chromatic adaptation

Our eyes can adjust to different lighting. For example, a white piece of paper looks white even under blue, pink, or purple light because our brain makes adjustments. This helps us see things more clearly, no matter how the light changes. This adjustment is important in photography and image editing, where tools like those in Adobe Photoshop help make pictures look right under different lighting conditions.

Color vision in nonhumans

Many animals can see colors differently than humans. Bees and other insects can see ultraviolet light, which helps them find nectar in flowers. Birds can also see ultraviolet light and some red colors, though not as well as humans.

Most mammals, like dogs and cats, have less color vision than humans, usually seeing only two main colors. However, some primates, like monkeys and apes, have color vision similar to humans. Many birds, fish, and insects have even better color vision than humans, with some seeing up to four or more colors.

Evolution

Main article: Evolution of color vision

Color vision has developed over time mainly to help animals find food. For example, in leaf-eating primates, color helps them spot the right leaves to eat. Birds also use color to find specific flowers. Animals that are active at night, like some mammals, don’t need great color vision because it’s too dark for their eyes to see colors well.

Some animals, including birds, fish, and insects, can see ultraviolet light, which is a type of light invisible to humans. This helps them find food, recognize each other, and stay safe while moving quickly.

Mathematics of color perception

A physical color is made up of different pure colors that we can see. Scientists think of all these possible colors as a very big space with many dimensions.

The CIE 1931 xy chromaticity diagram with a triangle showing the gamut of the Adobe RGB color space. The Planckian locus is shown with color temperatures labeled in kelvins. The outer curved boundary is the spectral locus, with wavelengths shown in nanometers. Note that the colors in this file are specified in Adobe RGB. Areas outside the triangle cannot be accurately rendered because they are out of the gamut of Adobe RGB, therefore they have been interpreted. Note that the colors depicted depend on the color space of the device you use to view the image (number of colors on your monitor, etc.), and may not be a strictly accurate representation of the color at a particular position.

When we see a color, it depends on how three types of special cells in our eyes react to the light. We can think of the color we see as a point in a three-dimensional space. By studying how these cells react to different colors, scientists can create models that help explain how we perceive color. This helps us understand why different combinations of light can look the same to our eyes.