Color blindness — more accurately called color vision deficiency — is far more common than most people realize. It affects approximately 8 percent of men and 0.5 percent of women of Northern European descent, meaning roughly 1 in 12 men has some degree of color vision deficiency. Despite the familiar term “color blind,” the vast majority of people with this condition do not see in black and white. They perceive color, but certain shades that other people easily distinguish are difficult or impossible for them to tell apart.
How Color Vision Works
The retina contains two types of light-sensitive cells: rods and cones. Rods handle low-light vision and do not perceive color. Cones are concentrated in the central part of the retina (the macula) and are responsible for color perception. There are three types of cones, each most sensitive to a different part of the spectrum — roughly corresponding to red, green, and blue wavelengths. Normal color vision results from the brain comparing signals from all three cone types.
Color vision deficiency occurs when one or more cone types is absent, present in reduced numbers, or contains abnormal photopigment that responds to a different range of wavelengths than normal.
Types of Color Vision Deficiency
Red-green color blindness is by far the most common type and is caused by abnormalities in either the red-sensitive (protan) or green-sensitive (deuteran) cones. People with red-green deficiency have difficulty distinguishing reds, greens, oranges, browns, and certain shades of yellow and purple from each other. The severity ranges from mild (deuteranomaly or protanomaly, where affected cones are present but abnormal) to severe (deuteranopia or protanopia, where one cone type is entirely absent).
Blue-yellow color blindness (tritanopia or tritanomaly) is much rarer and affects the blue-sensitive cones. People with this type have difficulty distinguishing blue from green and yellow from violet or red.
Complete color blindness (achromatopsia) — seeing only in shades of grey — is extremely rare and is typically accompanied by severe light sensitivity and reduced visual acuity.
What Causes Color Blindness?
The most common form of color vision deficiency is inherited. The genes encoding the red and green photopigments are located on the X chromosome, which is why red-green color blindness is far more prevalent in men (who have one X chromosome) than women (who have two and are often carriers without being affected). A woman must inherit the defective gene from both parents to be color blind.
Color vision deficiency can also be acquired rather than inherited. Diseases affecting the retina or optic nerve — including macular degeneration, glaucoma, and diabetic retinopathy — can damage color-sensitive cells. Certain medications, including some used to treat heart disease, blood pressure, and infections, can temporarily or permanently affect color perception. Aging also gradually reduces color sensitivity, particularly for blues.
How Color Vision Is Tested
The most widely used screening test is the Ishihara plate test, which consists of circles composed of colored dots. People with normal color vision see a number embedded in the pattern; those with color vision deficiency see a different number or nothing at all. The Ishihara test is sensitive for red-green deficiency but does not assess blue-yellow deficiency or quantify severity precisely.
More comprehensive testing, including the Farnsworth-Munsell 100 Hue Test or the Farnsworth D-15 arrangement test, can characterize the type and severity of color deficiency more accurately. Our free color vision test provides a quick preliminary screening, though it does not replace a formal clinical evaluation.
Living with Color Vision Deficiency
Most people with color vision deficiency adapt well to daily life. Practical strategies include labeling clothing by color to avoid mismatches, using apps that identify colors through the phone’s camera, paying attention to position rather than color for traffic signals, and choosing high-contrast design tools in professional settings. Specialized filter glasses (such as EnChroma lenses) can enhance the perceived distinction between certain shades for some people with red-green deficiency, though they do not restore normal color vision and vary widely in effectiveness.
Color vision deficiency is assessed during a comprehensive eye exam. Visit our eye care services page to schedule an evaluation or explore our free vision tools to check your color vision at home.