The most common form of color blindness is red-green color blindness, which accounts for roughly 99% of all cases. Within that category, the single most common subtype is deuteranomaly, a reduced sensitivity to green light. About 1 in 12 men (8%) and 1 in 200 women have some form of color vision deficiency, and the vast majority fall into this red-green category.
What Deuteranomaly Actually Looks Like
People with deuteranomaly don’t see the world in black and white. Their eyes still detect color, but the cone cells responsible for picking up green light don’t work as well as they should. The result is that greens, yellows, oranges, and reds can blur together or look muddy. A bright green traffic light might appear almost white. Ripe and unripe fruit can look the same. The difference between a red pen and a brown pen might be invisible.
Most people with deuteranomaly have a mild version and may not even realize they see colors differently until they take a screening test. Children with the condition sometimes smell food before eating it, even dishes they’ve had before, because they can’t rely on color to tell them what’s on the plate. For the majority of people, though, mild red-green color blindness doesn’t interfere with daily routines in a significant way.
The Full Spectrum of Red-Green Subtypes
Red-green color blindness isn’t one condition. It’s a group of four related subtypes, and they vary in both severity and frequency. Among color-blind men, the breakdown looks roughly like this:
- Deuteranomaly (about 5% of men): Reduced sensitivity to green light. Colors shift toward the red end of the spectrum. This is the mildest and most common form overall.
- Protanomaly (about 1% of men): Reduced sensitivity to red light. Reds appear darker and can be confused with greens or browns.
- Deuteranopia (about 1% of men): Complete inability to detect green light. More severe than deuteranomaly, with a narrower range of distinguishable colors.
- Protanopia (about 1% of men): Complete inability to detect red light. Red objects can appear almost black in dim lighting.
To put those numbers in perspective, in a group of 1,000 men, roughly 80 to 85 would have some color vision deficiency. About 62 of them would have deuteranomaly specifically. The remaining would be split among the other three types, with roughly 11 to 13 men in each group.
Why Men Are Affected Far More Often
The genes that control red and green cone cells sit on the X chromosome. Since men have only one X chromosome (paired with a Y), a single faulty copy of the gene is enough to cause color blindness. Women have two X chromosomes, so a working copy on the second X can compensate for a defective one on the first. For a woman to be red-green color blind, both of her X chromosomes need to carry the altered gene, which is far less likely.
This inheritance pattern also means fathers can’t pass red-green color blindness to their sons. A father gives his son a Y chromosome, not an X. Instead, the trait passes through mothers. A woman who carries one copy of the gene won’t be color blind herself, but she has a 50% chance of passing it to each of her sons. This is why the condition often seems to skip a generation, going from a color-blind grandfather through a carrier daughter to an affected grandson.
Other, Rarer Types of Color Blindness
Blue-yellow color blindness (tritanomaly and tritanopia) exists but is extremely rare and follows a different inheritance pattern. It’s not linked to the X chromosome, so it affects men and women at roughly equal rates.
Total color blindness, known as achromatopsia, is rarer still. People with this condition see only in shades of gray and typically have other symptoms like extreme light sensitivity and reduced visual sharpness. It affects somewhere between 1 in 30,000 and 1 in 50,000 people worldwide. Compared to deuteranomaly, which affects 1 in 20 men, achromatopsia is vanishingly uncommon.
Living With Red-Green Color Blindness
There is currently no cure for inherited color blindness. Gene therapy has shown promising results in animal studies, but it hasn’t been tested in humans for this condition. Some clinical research is exploring light-based therapies, though these remain experimental and far from standard treatment.
In practice, most people with deuteranomaly adapt without much difficulty. They learn to read traffic lights by position (top, middle, bottom) rather than color. They label clothing or ask for help matching outfits. Digital tools and phone apps can identify colors in real time. Many workplaces and websites now follow accessibility guidelines that avoid relying on red-green contrast alone to convey information, using patterns, labels, or different color palettes instead.
Where color blindness matters most is in certain careers. Pilots, electricians, and some military roles require accurate color discrimination, and screening tests can disqualify candidates with significant deficiencies. For most other aspects of life, the condition is a minor inconvenience rather than a serious limitation. Many people don’t discover they have it until well into adulthood.