Many people take their color vision for granted, but this sense is actually the result of specialized cells within the eye. These cells, located in the retinas, are called cone cells. Cone cells contain pigments that have different spectral sensitivities, making it possible to perceive color and distinguish one hue from another. These cones are named according to the wavelengths they perceive. S cones help with the perception of short wavelengths, M cones help perceive medium wavelengths, and L cones aid in the perception of long wavelengths. The nervous system also plays a role in color vision, as the optic nerve transmits messages from the retina to the brain. These messages help living organisms process visual information, making it possible to see images and colors.
- Human Vision and Color: This resource explains how humans perceive color.
- The Rods and Cones of the Human Eye: This article explains how the rods and cones of the eye aid in color perception.
Monochromacy is known as total color blindness. This condition results from the absence of retinal cones in the eye or defects of the retinal cones in the eye. Organisms with monochromacy are completely unable to distinguish colors. There are two different types of monochromacy. Cone monochromacy occurs when an organism only has one type of cone in the eye. This type of monochromacy can be further classified as red cone monochromacy, blue cone monochromacy, or green cone monochromacy. Rod monochromacy is when the retina only has rods. Organisms with this type of monochromacy only see shades of gray. Cetaceans and pinnipeds, two types of sea mammals, are cone monochromats. Some people are also monochromats, but true monochromacy is rare in humans.
- Color Perception: This resource explains how color is perceived and details the different color vision deficiencies that affect living organisms.
- Blue Cone Monochromacy: This article explains the effects of blue cone monochromacy in humans.
- Color Blindness: This resource discusses color blindness and includes information about rod monochromacy.
Dichromatic organisms only have two types of cone cells in the eyes. This means that they have difficulty distinguishing certain colors from other colors. There are three types of dichromacy: protanopia, deuteranopia, and tritanopia. Protanopia causes difficulty perceiving reds and other long wavelengths. Organisms with this type of dichromacy perceive reds as gray or beige. This condition is also called red-green color blindness. Deuteranopia makes it difficult to perceive colors with medium wavelengths. Organisms with this condition cannot see reds and greens accurately, but they can distinguish them from other colors. Tritanopia is a rare form of color blindness that makes it difficult to perceive colors with short wavelengths. Organisms with this condition have difficulty distinguishing between blue and yellow. Many mammals are dichromats, with the exception of marsupials, sea mammals, owl monkeys, and primates.
- Dichromacy Explorer: This resource allows users to experiment with different wavelengths to see the effects of dichromacy.
- Primate Color Vision: This scientific resource discusses color perception in primates.
Trichromats have three different channels for perceiving color. These channels come from the three different types of cones in the eye. Most humans are trichromats, along with howler monkeys and most primates. Scientists believe that marsupials are also trichromats. Organisms with trichromacy need three different wavelengths to perceive the normal range of colors. Some people develop anomalous trichromacy, which means they have difficulty distinguishing between certain hues. Protanomaly and deuteranomaly are types of red-green anomalous trichromacy. Tritanomaly affects the perception of blues and yellows.
- Anomalous Color Perception (PDF): This article discusses some of the anomalies that affect color perception.
- Trichromatic Color Vision in Primates (PDF): This article discusses trichromatic color vision in some primate species.
Tetrachromats have four different channels for perceiving color, which means they have four different types of cone cells. Organisms with tetrachromacy have a slight advantage over trichromatic organisms in the wild. Several species of fish, insects, reptiles, arachnids, and amphibians are thought to be tetrachromats. These species can perceive different hues that would look identical to humans and other trichromats.
- Looking for Madam Tetrachromat: This article discusses the fascinating case of a woman thought to have tetrachromacy.
Pentachromats have five different channels for capturing, transmitting, and perceiving color. Organisms with pentachromacy have five different types of cone cells in their retinas. Some scientists suspect that some pentachromats may even have more than five types of cone cells. Butterflies and some bird species have five or more color receptors in the retinas, but scientists have been unable to confirm if they are pentachromats. Lampreys, a type of eel, may also be pentachromats.