Color blindness is a condition where your eyes cannot distinguish certain colors the way most people do. It affects roughly 8% of men and 0.5% of women of Northern European descent, making it one of the most common inherited vision differences in the world. Despite the name, most people with color blindness aren’t living in black and white. They see color, just a narrower or shifted version of it.
How Normal Color Vision Works
Your retina contains three types of cone cells, each sensitive to a different range of light wavelengths. These are commonly called red, green, and blue cones, though scientists refer to them as long (L), medium (M), and short (S) wavelength cones. Each type contains a different light-sensitive protein called an opsin that responds most strongly to its particular slice of the spectrum.
Here’s the key detail: a single cone cell is actually color blind on its own. It simply counts how many photons hit it, with no way to determine what color those photons represent. Your brain creates the experience of color by comparing the signals from all three cone types simultaneously. When one type is missing or altered, the comparison breaks down, and certain colors become difficult or impossible to tell apart.
Types of Color Blindness
Color blindness falls into three broad categories based on which cone cells are affected.
Red-Green Color Blindness
This is by far the most common form. It comes in four subtypes:
- Deuteranomaly: The most common type overall. Green-sensitive cones respond to slightly wrong wavelengths, making some greens look more red. It’s typically mild and rarely interferes with daily life.
- Protanomaly: Red-sensitive cones are altered, making reds appear greener and less bright. Also mild in most cases.
- Deuteranopia: Green-sensitive cones are missing entirely, making it impossible to distinguish red from green.
- Protanopia: Red-sensitive cones are missing entirely, with a similar inability to separate red and green.
The two milder forms (deuteranomaly and protanomaly) mean the cones are present but slightly “mis-tuned.” The two severe forms (deuteranopia and protanopia) mean an entire cone type is absent, collapsing a three-channel color system down to two.
Blue-Yellow Color Blindness
Known as tritan deficiency, this type affects the short-wavelength (blue) cones. It makes it hard to tell blue from green and yellow from violet. Tritan deficiency is much rarer than the red-green type and follows a different inheritance pattern, since the gene responsible sits on chromosome 7 rather than the X chromosome. That means it affects men and women at roughly equal rates.
Total Color Blindness
Complete color blindness, called achromatopsia, is the rarest form. People with this condition see the world largely in shades of gray. It often comes with additional symptoms: sensitivity to light, rapid involuntary eye movements, and reduced visual sharpness. Achromatopsia results from none of the cone types working properly, leaving the retina dependent on rod cells, which detect light and dark but not color.
Why It’s Far More Common in Men
The genes for both the red-sensitive and green-sensitive cone pigments sit right next to each other on the X chromosome. Men have only one X chromosome, so a single defective copy of either gene is enough to cause color blindness. Women have two X chromosomes, meaning a working copy on the second X can compensate for a faulty one on the first. A woman would need defective copies on both X chromosomes to be affected, which is why only about 0.4% to 0.5% of women have red-green color blindness compared to 8% or more of men in European populations.
The genes for the red and green pigments are also remarkably similar in their DNA sequence, which makes them prone to shuffling and swapping during cell division. These genetic rearrangements are the root cause of most inherited red-green color blindness.
Prevalence Varies by Ethnicity
Color blindness is not evenly distributed across the globe. Populations of European descent have the highest rates: around 8% to 9% of men in Northern Europe, the United States, and Russia. Rates in East Asian populations are moderate, roughly 4% to 7% among Chinese men and about 4% among Japanese men. Rates in African and Pacific Islander populations tend to be lower, with studies reporting 1.7% in the Democratic Republic of the Congo, 2.2% in South Africa, and just 0.8% among Fijian men. Aboriginal Australians show a rate of about 1.9%.
Color Blindness You Weren’t Born With
Not all color blindness is genetic. A range of eye diseases and medical conditions can damage color vision over time. Glaucoma, cataracts, age-related macular degeneration, and optic nerve inflammation can all degrade color perception, typically affecting blue-yellow discrimination first.
Certain medications also carry this risk. Hydroxychloroquine, used for autoimmune conditions like lupus and rheumatoid arthritis, can cause blue-yellow color deficits in early stages of retinal toxicity that progress to red-green problems with continued use. Notably, the color changes from this drug may not reverse even after stopping treatment, because the compound lingers in the retina for years. Ethambutol, an antibiotic used to treat tuberculosis, also causes blue-yellow color shifts by damaging the optic nerve, though color vision typically recovers once the medication is discontinued.
Acquired color blindness differs from the inherited kind in a few ways. It can affect one eye more than the other, it may worsen over time, and it sometimes responds to treatment of the underlying cause.
How It’s Diagnosed
The most familiar screening tool is the Ishihara plate test: a series of cards filled with colored dots that form numbers or symbols visible only to people with normal color vision. If you can’t read some of the numbers, the pattern of your errors reveals which type of deficiency you have. It’s quick and effective for catching red-green problems but doesn’t assess blue-yellow vision well.
For a more precise measurement, the Farnsworth-Munsell 100 Hue test asks you to arrange 100 colored tiles in order as the hue gradually shifts. The pattern of errors maps exactly where your color discrimination breaks down and how severely. This test is commonly used for occupational screening or monitoring medication-related color changes.
Daily Life and Career Considerations
For the majority of people with color blindness, the condition is mild enough that it rarely causes serious problems. You might struggle to tell ripe from unripe fruit, misread color-coded charts, or have trouble picking out matching clothes. Traffic lights are a common concern, but most people with red-green deficiency learn to rely on the position of the light (top, middle, bottom) rather than the color itself.
Certain careers do have strict color vision requirements. Pilots, ship navigators, train operators, and electricians all need to identify color-coded signals or wiring reliably. Some police and military roles also screen for color vision. These restrictions exist because misreading a signal light or wire color in these fields creates genuine safety risks.
In everyday workplaces, accessibility has improved. Many apps and operating systems now offer color-blind modes, and designers increasingly use patterns, labels, or brightness differences alongside color to convey information.
Do Color-Correcting Glasses Work?
Special filter glasses, such as those made by EnChroma, use selective lens coatings that block specific wavelengths of light to increase the contrast between red and green. The emotional reaction videos online are compelling, but the clinical evidence is more nuanced. A controlled study found that EnChroma filters did not clearly improve color discrimination scores for most users. The one exception was people with protanopia (missing red cones), who showed some improvement on a pattern-recognition task. For people with the more common deutan deficiencies, the filters actually shifted the type of errors made rather than reducing them. On a color-naming task, the glasses impaired performance for all participants, particularly for cyan-colored objects.
That doesn’t mean the glasses are useless for quality of life. Many users report that colors feel more vivid or distinct, even if their measurable accuracy on clinical tests doesn’t change much. But they’re not a correction in the way prescription eyeglasses correct blurry vision. They alter the input your eyes receive without fixing the underlying cone cell limitation.