What Are the 7 Types of Color Blindness?

Not one condition, but seven

"Color blind" describes seven different conditions, not one. All seven come from the same place: the eye's cone cells, which sense color, respond to light differently than they do in someone with typical color vision. Depending on which cone is affected and how, the result is one of three families.

Trichromacy, the typical case

A person with typical color vision has three working cone types: one tuned to long wavelengths (perceived as red), one to medium wavelengths (green), and one to short wavelengths (blue). The brain compares the signal from all three to build the full range of visible color. This is called trichromacy, and it is the baseline every type of color blindness deviates from.

The four red-green types

Red-green deficiency is by far the most common family, and it splits into two mechanisms: a cone that works but is shifted (anomalous trichromacy), and a cone that is missing entirely (dichromacy).

Deuteranomaly alone accounts for most cases of color blindness worldwide. The "anomaly" types are usually milder than the "opia" types, because a shifted cone still contributes some signal, while an absent cone contributes none.

The two blue-yellow types

Tritanomaly (a shifted blue cone) and tritanopia (an absent blue cone) affect far fewer people, roughly 1 in 10,000, and unlike the red-green types, they are not linked to a specific gene on the X chromosome. Blue-yellow deficiency can also be acquired later in life, through aging, certain medications, or conditions affecting the eye, rather than only inherited at birth.

Complete color blindness

Monochromacy, also called achromatopsia, is the rarest and most severe type, affecting roughly 1 in 30,000 people. None of the three cone types function, so vision relies entirely on rod cells, which do not distinguish color at all. The world appears in shades of gray, and it is often accompanied by light sensitivity and reduced sharpness, since cones also handle fine detail.

Why men are affected far more often than women

The genes for the red and green cones sit on the X chromosome. A man has one X chromosome, so a single altered gene is enough to change his color vision. A woman has two X chromosomes, so a second, typically functioning copy usually compensates. This is why red-green color blindness affects about 1 in 12 men but only about 1 in 200 women. Blue-yellow deficiency and monochromacy sit on different chromosomes, so they do not follow this same pattern and affect both sexes at similar rates.

How the Ishihara test identifies each type

The Ishihara test, published by Shinobu Ishihara in 1917, remains the standard first screening for red-green deficiency. Each plate shows a number formed by dots of one color, hidden inside a field of dots in a different color, chosen so the two colors are equally bright. Someone with typical color vision separates them by hue and reads the number. Someone with a red-green deficiency sees mostly dots of similar brightness and cannot find the shape. Because it targets brightness confusion specifically in the red-green range, the test does not reliably detect blue-yellow deficiency or monochromacy, which need separate plates or instruments.

What this guide does not do

This page explains what the seven types are and how they work. It is not a vision test, it does not diagnose which type a reader has, and it is not a substitute for an eye care professional. Diagnosing a specific type requires a clinical test, not an article.

Seeing the difference

Reading the mechanism is one thing; seeing what it does to actual colors is another. Our color palette generator simulates how a palette appears under three of these seven types, protanopia, deuteranopia and tritanopia, the ones with the biggest visual effect, using the Brettel and Viénot color math. The four milder or rarer types, protanomaly, deuteranomaly, tritanomaly and monochromacy, are not simulated there yet.