Color blindness falls into three main categories: red-green, blue-yellow, and complete color blindness. Within those categories, there are several distinct subtypes, each affecting vision differently. About 1 in 12 men and 1 in 200 women have some form of color vision deficiency, totaling roughly 300 million people worldwide.
Red-Green Color Blindness
Red-green deficiency is by far the most common category, and it breaks down into four subtypes based on which cone cells in the eye are affected and how severely.
Deuteranomaly is the single most common form, affecting about 5% of males. The green-sensitive cones in the eye still work but respond slightly off from where they should on the light spectrum. The result is that certain shades of green look more red. Most people with deuteranomaly consider it mild, and many don’t realize they have it until they’re tested.
Protanomaly is similar but affects the red-sensitive cones instead, occurring in about 1% of males. Certain reds appear more green and less bright. Like deuteranomaly, it’s typically mild enough that it doesn’t interfere much with daily life. Both deuteranomaly and protanomaly are forms of “anomalous trichromacy,” meaning all three types of cone cells are present and functioning, but one type is shifted slightly out of alignment.
Protanopia and deuteranopia are more severe. In these forms, one type of cone cell is completely nonfunctional, leaving only two working types. Protanopia (about 1% of males) means no red cone function at all, while deuteranopia (about 1% of males) means no green cone function. Both make it impossible to distinguish red from green reliably, not just difficult.
Why Men Are Affected Far More Often
The genes responsible for red and green cone cells sit on the X chromosome, right next to each other. Because these two genes are so similar, they sometimes swap material when being passed from parent to child. That swapping can delete portions of one gene or create a hybrid gene that doesn’t produce a normal pigment. Men have only one X chromosome, so a single defective copy is enough to cause color blindness. Women have two X chromosomes, so a working copy on the second chromosome usually compensates.
This is why roughly 8% of men have some form of color vision deficiency while the rate in women is closer to 0.5%.
Blue-Yellow Color Blindness
Blue-yellow deficiency is dramatically rarer than the red-green type. The gene for blue cone cells sits on chromosome 7, not the X chromosome, which means it affects men and women at equal rates. But those rates are extremely low.
Tritanomaly affects roughly 1 in 1,000,000 people. The blue cones are present but shifted, making it hard to tell blue from green and yellow from red. Tritanopia is slightly more common at about 1 in 100,000 but still rare. It involves a complete loss of blue cone function, which scrambles several color pairs: blue and green, purple and red, yellow and pink all become difficult to distinguish. Colors also appear less bright overall.
Complete Color Blindness
Complete color blindness, called monochromacy or achromatopsia, is the rarest and most disabling form. People with this condition see the world in shades of gray, or close to it, because their cone cells are absent or nonfunctional.
One form, blue cone monochromacy, leaves only the blue cones and rod cells working while the red and green cones fail. Vision relies heavily on the rods, which are designed for low-light conditions rather than color or detail. The result goes beyond just losing color. People with this condition often experience significantly reduced visual sharpness, sensitivity to light that can be painful, nearsightedness, and involuntary rapid eye movements.
Rod monochromacy, where no cone cells function at all, is even more severe. All color perception is lost and vision depends entirely on rod cells, which perform poorly in bright light and offer low resolution. Bright environments can be genuinely debilitating.
Color Blindness You Aren’t Born With
Not all color vision deficiency is genetic. A range of medical conditions can damage color perception later in life, including diabetes, glaucoma, macular degeneration, multiple sclerosis, Parkinson’s disease, and Alzheimer’s disease. Chronic alcoholism and sickle cell anemia also carry risk. Certain medications, particularly hydroxychloroquine (used for rheumatoid arthritis), can alter color vision as a side effect. Physical trauma to the eye from injury, surgery, or radiation can do the same.
Acquired color blindness differs from the inherited kind in a few ways. It can affect just one eye, it may worsen over time, and it often involves blue-yellow confusion rather than the red-green pattern typical of inherited deficiency. If your color perception changes as an adult, that’s worth investigating because it can signal an underlying condition.
How Color Blindness Is Diagnosed
The most familiar screening tool is the Ishihara test, where you look at circles filled with colored dots and try to read a number hidden in the pattern. It’s fast and effective, but it only detects red-green deficiency. The Richmond HRR test uses a similar dot-plate format but can identify both red-green and blue-yellow problems and rate their severity from mild to severe.
The most precise diagnostic tool is an anomaloscope. You look through an eyepiece at a circle split into two halves of different color and use knobs to adjust one half until you think it matches the other. People with color deficiency will accept matches that look obviously wrong to someone with normal vision. This is considered the gold standard for red-green diagnosis.
For a broader assessment, the Farnsworth-Munsell 100-Hue test asks you to arrange colored caps in order. It picks up both red-green and blue-yellow deficiencies and reveals how your color discrimination compares to the general population. A shorter version, the D-15, covers the same ground more quickly.
Careers With Color Vision Requirements
Certain jobs require reliable color discrimination, and failing a screening test can limit your options. Aviation is the most structured example. The FAA requires pilots to pass an approved color vision screening. As of January 2025, this is a one-time computer-based test. Pilots who fail every approved test can still fly, but their medical certificate is restricted to daytime visual flight rules only, which rules out instrument flying and nighttime operations. Color-correcting lenses are not accepted as a workaround.
Air traffic control, law enforcement, electrical work, and some military roles also have color vision requirements, though the specific standards vary. The common thread is any job where misreading a color-coded signal could create a safety hazard. If you know you have color vision deficiency and are considering one of these fields, getting tested early saves time and frustration.
Living With Color Vision Deficiency
For the vast majority of people with color blindness, the condition is mild. Deuteranomaly, the most common type, rarely disrupts everyday life in a significant way. Many people discover they have it only through routine screening.
Smartphone apps can now identify colors in real time through the camera, which helps with tasks like picking matching clothes or reading color-coded charts. Some tinted glasses and contact lenses enhance contrast between colors that are normally confused, though they don’t restore normal color vision and aren’t accepted for occupational screenings. Digital accessibility settings on phones, computers, and video games increasingly offer colorblind-friendly modes that shift problem colors into distinguishable ranges.
For the small number of people with achromatopsia, gene therapy trials have shown early promise. A 2022 report from ongoing clinical trials that began in 2016 found that two pediatric participants experienced improved cone function and cone-supported vision after treatment. These trials are still in progress and limited to the most severe forms of color blindness, but they represent the first real steps toward biological correction.