Types of Color Blindness
"Color blindness" rarely means seeing no color. Far more often it means certain colors are hard to tell apart. Here are the main types.
Red-green deficiency (the common one)
Red-green deficiency is by far the most common form. It comes in two related types, depending on which cone cells are affected:
Deutan
Green-weak (deuteranomaly / deuteranopia)
The green-sensitive cones are shifted or missing. Greens, browns, oranges and reds can blur together. This is the most common type.
Protan
Red-weak (protanomaly / protanopia)
The red-sensitive cones are affected. Similar confusions to deutan, but reds also look darker, so red signals and warnings can be easy to miss.
Tritan
Blue-yellow (tritanomaly / tritanopia)
The blue-sensitive cones are affected. Blues and greens, and yellows and pinks, become hard to separate. This type is rare and is more often acquired than inherited.
How common is it?
About 1 in 12 men and about 1 in 200 women have red-green color vision deficiency (NHS). The large difference is because the most common forms are inherited on the X chromosome. Blue-yellow deficiency is much rarer and affects men and women about equally.
Monochromacy (very rare)
A small number of people have little or no color vision at all (monochromacy or achromatopsia). It's uncommon and usually comes with other vision differences, such as light sensitivity.
What a diagnosis actually involves
An eye care professional confirms color vision deficiency with calibrated tools: printed plate books under controlled lighting, arrangement tests like the D-15, or an anomaloscope for precise typing. An online screen can point you in the right direction, but it can't replace that.