Color blindness — also known as color vision deficiency (CVD) — is a condition where you don’t see colors in the traditional way. This can happen if certain cells known as photoreceptors, or more specifically cones, in your eyes are missing or not working correctly. These cones typically allow you to see each color on the rainbow. If you have color blindness, you might not see each of these colors.
Don’t confuse color blindness with a type of blindness (a condition where you have limited or no sight) — color blindness is simply a change in the way your eyes see color.
We all see a continuum (range) of colors, but which ones we see depends on how well our photoreceptors function. Photoreceptors are cells within your eyes that respond to specific wavelengths of light. Everyone sees color slightly differently, and the way we see colors may also change as we age if we develop certain age-related eye conditions such as cataracts.
When we see different colors, what we’re really perceiving is different wavelengths of light. Your eyes contain photoreceptors (cells) that process light entering the eye to help you perceive color. Rods detect differences between dark and light. Cone cells detect colors when lighting conditions are bright enough. Each wavelength corresponds to a different shade in the visible spectrum of light. Reds are the longest wavelengths, greens are medium and blues are the shortest.
Generally, people with color blindness have difficulty articulating what they perceive, but scientists suggest the typical colorblind person might see colors as varying shades of blue and yellow. For example, what a color-normal person calls purple and what a colorblind person calls purple may not be the same color. Or, both people may look at the same color and call it different things.
A person's color vision falls into one of the following categories:
Full color vision/Trichromacy: If you were born with normal-functioning color pigments in all three cone types in your eyes, you’re a trichromat. You’d see six colors in your rainbow: red, orange, yellow, green, blue and violet.
Color vision deficiency/Dichromacy: If you were born with missing or malfunctioning (not working) cones of one of the three types in your eyes, you’re a dichromat or dichromatous. What colors you see depends upon which cones are missing or malfunctioning.
If you’re a dichromat, there are several specific types of color deficiency you might experience, including:
Red-Green Color Deficiency:
Blue-Yellow Color Deficiency:
Fully Color Blind/Monochromacy: If you’re a monochromat, you have a very limited or no ability to see color. Your vision might be a lot like watching a black and white television or an old black and white movie. Your rainbow would appear in varying shades of gray.
Monochromats come in two types:
Color blindness is uncommon, but it does run in families. This means that if other members of your family have experienced color blindness, you’re more likely to have it too. Color blindness can happen in both men and women, but it’s much more commonly seen in men. This is because color blindness is passed down through your genetic code.
Sometimes, color blindness can also show up later in life. In some cases, it may have been present at birth but not noticed until later. In other cases, injuries or diseases of the eye can cause malfunctions in the parts of the visual system that allow color vision, including not just the photoreceptors but also the nerves and some retinal layers.
Red-green color blindness, the most common form by far, is a genetic mutation that is passed to children on the X chromosome. At conception, an egg carries an X chromosome and the sperm cell can carry either an X chromosome or a Y chromosome. If you have an XX chromosome pair, the resulting baby will be female. If you have an XY chromosome pair, the baby will be male. The gene responsible for color blindness is located on the X chromosome. In other words, red-green color blindness is an X-linked recessive condition. If a female inherits one normal color vision gene and one mutated gene, she won’t be red-green color blind, because it’s a recessive trait. If she inherits two mutated color vision genes, she’ll be color red-green blind.
Since boys have only one X chromosome, their chance of inheriting red-green color blindness is much greater. Boys always inherit their X chromosome from their mother. If mom has red-green color blindness, or if mom’s dad is red-green colorblind, her son will be too.