What Is Color Blindness?
Color blindness — more accurately called color vision deficiency (CVD) — is the reduced ability to distinguish between certain colors. Despite the name, most people with color blindness are not entirely unable to see color; rather, they perceive a narrower or shifted color spectrum compared to people with typical color vision.
According to the National Eye Institute, approximately 8% of men (1 in 12) and 0.5% of women (1 in 200) with Northern European ancestry are affected by some form of color blindness. Globally, that accounts for roughly 300 million people.
Key Statistic
Approximately 8% of men (1 in 12) and 0.5% of women (1 in 200) are affected by some form of color vision deficiency — totaling around 300 million people worldwide.
How Color Vision Works
The human eye contains two types of photoreceptors in the retina: rods, which detect light and dark and are responsible for peripheral and night vision, and cones, which detect color. Most people have three types of cone cells: long-wavelength (L-cones, sensitive to red), medium-wavelength (M-cones, sensitive to green), and short-wavelength (S-cones, sensitive to blue).
The brain combines signals from all three cone types to produce the full color spectrum we perceive. Color blindness occurs when one or more of these cone types is absent, defective, or has a shifted peak sensitivity — typically due to a genetic mutation in the photopigment protein.
Types of Color Blindness
Red-Green Color Blindness is by far the most common form and includes several subtypes. Deuteranopia and deuteranomaly involve deficiency in M-cones (green), while protanopia and protanomaly involve deficiency in L-cones (red). People with red-green color blindness typically struggle to distinguish reds, greens, and browns from each other, and may confuse orange with yellow or red.
Blue-Yellow Color Blindness (tritanopia and tritanomaly) is much rarer, affecting fewer than 1 in 10,000 people, and involves deficiency in S-cones. People with this type confuse blue with green and yellow with violet.
Total Color Blindness (achromatopsia) is extremely rare and involves the absence of functioning cone cells entirely, resulting in the perception of only black, white, and shades of gray. It is often accompanied by extreme light sensitivity and reduced visual acuity.
Causes and Genetics
The most common forms of color blindness are inherited through an X-linked recessive pattern, which is why men are far more frequently affected — they have only one X chromosome, so a single faulty gene is sufficient. Women have two X chromosomes, so they typically need faulty genes on both copies to be affected, though they can be carriers.
Less commonly, color blindness can be acquired rather than inherited. Conditions that damage the retina or optic nerve — including glaucoma, macular degeneration, diabetic retinopathy, and Parkinson's disease — can cause color vision changes. Certain medications (notably hydroxychloroquine and some antipsychotics) and prolonged exposure to some industrial chemicals are also known causes.
The Ishihara Test: What It Tells You
The Ishihara color vision test, developed by Japanese ophthalmologist Shinobu Ishihara in 1917, remains the most widely used screening tool for red-green color blindness. The test consists of a series of circular plates (pseudoisochromatic plates) containing colored dots arranged to form numbers or patterns that are visible to people with normal color vision and invisible (or appear differently) to those with color vision deficiency.
Online versions of the Ishihara test — like the one on this site — can serve as a useful initial screen, but a formal diagnosis should be made by an eye care professional using standardized, calibrated printed plates. Screen calibration, lighting conditions, and screen glare can all affect online test accuracy.
About Online Tests
Online Ishihara tests are useful for initial screening, but screen calibration and lighting conditions affect accuracy. For a formal diagnosis, visit an optometrist who can administer standardized printed plates under controlled conditions.
Frequently Asked Questions
Can color blindness be cured? There is currently no cure for inherited color blindness. EnChroma glasses use a special filter to shift wavelengths and help some people distinguish colors more easily, but they don't restore normal color vision and don't work for everyone.
Does color blindness affect driving? People with most types of color blindness can drive safely — they learn to rely on the position of traffic lights rather than the color alone. However, severe color deficiency may be disqualifying for commercial vehicle licenses in some jurisdictions.
Can color vision deficiency develop later in life? Yes — acquired color blindness can develop from eye disease, medication side effects, or neurological conditions. Unlike inherited color blindness, acquired forms may affect one eye differently from the other and can sometimes be reversed if the underlying cause is treated.
Living With Color Blindness
Most people with color blindness adapt their daily lives without significant difficulty. Common strategies include labeling colored wires or clothing by name, using apps like Seeing AI or Color Blind Pal to identify colors in real time, and choosing high-contrast color combinations.
Color blindness can affect career choices — it may disqualify candidates from roles requiring accurate color discrimination, such as certain military positions, air traffic control, and some medical specialties. However, the range of unaffected careers is vast, and most people with color blindness live entirely normal professional lives.
Research into gene therapy for color vision deficiency is ongoing and has shown early promise in animal studies, offering hope for future treatments.