Color Blindness: Types and Testing
Most people called color blind can see color. They see some colors differently. Here is what the kinds are, who has them, and how they are properly tested.
Color blindness, or color vision deficiency, means seeing some colors differently from most people; very few people see no color at all. The red-green kinds are by far the most common and are usually inherited, affecting about 1 in 12 men and 1 in 200 women of Northern European ancestry. Blue-yellow kinds are rare. An eye doctor tests for it, usually starting with a color plate test, and there is no cure for the inherited kinds.
“Color blind” is a misleading name. The American Optometric Association points out that although the term is widely used, “very few people are completely color blind.” The National Eye Institute describes the condition more accurately: if you have it, “you see colors differently than most people”, and most of the time it “makes it hard to tell the difference between certain colors.” Its medical name is color vision deficiency. If you design charts or interfaces, the Color Blindness Simulator shows an approximation of how an image reads under three kinds of it.
The kinds, and what each one changes
The National Eye Institute groups color vision deficiency into three families. The names ending in “-anomaly” are milder forms, where a color is shifted; the names ending in “-anopia” are the stronger forms, where two colors cannot be told apart at all.
| Type | What the National Eye Institute says it does |
|---|---|
| Deuteranomaly (red-green) | "The most common type of red-green color vision deficiency. It makes certain shades of green look more red." |
| Protanomaly (red-green) | "Makes certain shades of red look more green and less bright." |
| Protanopia and deuteranopia (red-green) | "Make someone unable to tell the difference between red and green at all." |
| Tritanomaly (blue-yellow) | "Makes it hard to tell the difference between blue and green and between yellow and red." |
| Tritanopia (blue-yellow) | "Makes someone unable to tell the difference between blue and green, purple and red, and yellow and pink." |
| Complete (monochromacy, achromatopsia) | "You can't see colors at all." The Institute adds that "it's rare." |
The two mild red-green forms, the Institute notes, usually do not “get in the way of normal activities.”
How common it is
The figures quoted most often come from MedlinePlus Genetics, a service of the U.S. National Library of Medicine: red-green color vision deficiency occurs “in about 1 in 12 males and 1 in 200 females” among “populations with Northern European ancestry.” It adds that red-green defects “have a lower incidence in almost all other populations studied.”
The other kinds are much rarer. MedlinePlus Genetics puts blue-yellow defects at “fewer than 1 in 10,000 people worldwide”, affecting “males and females equally.”
Different sources give slightly different figures because they count different groups. The American Optometric Association, for example, says "about 8% of white males are born with some degree of color deficiency" and "approximately 0.5% of women" have it. Quote a figure together with the population it describes.
What causes it
For most people it is inherited. The National Eye Institute says “most people who have color vision deficiency are born with it”, because “the most common types of color vision deficiency are genetic.” Men are affected far more often than women by the red-green kinds, while the blue-yellow and complete kinds, the Institute says, “involve other chromosomes, so they affect people of different sexes equally.”
It can also start later in life. The Institute lists eye diseases such as “glaucoma or age-related macular degeneration”, “brain and nervous system diseases”, “some medicines — like Plaquenil”, and eye or brain injuries. It also notes that color vision “may also get worse as you get older — often because of cataracts.”
A change in how you see colors is worth taking seriously. The American Academy of Ophthalmology advises anyone whose color perception changes significantly to see an ophthalmologist.
How it is tested
Testing is done by an eye doctor. The National Eye Institute describes three tests:
- 1
The color plate test. Pictures made of colored dots, with a number or a path hidden in them. The American Optometric Association calls them "pseudoisochromatic plates". This is usually the first test.
- 2
The anomaloscope. "You'll look through an eyepiece at 2 lights that have different levels of brightness" and use knobs to try to make them match.
- 3
The hue test. Colored blocks to arrange "in rainbow order — from red to purple". The Institute notes it is often used "for people who need to have very accurate color vision for their jobs — like graphic designers."
ScreenTail does not offer a color vision test. The plates an eye doctor uses are printed cards, which MedlinePlus describes being held “14 inches (35 centimeters) from your face”; a screen shows its colors through its own settings, brightness and calibration, which differ from one screen to the next. If you want to know about your own color vision, an eye doctor is the place to ask.
What helps
The National Eye Institute is plain about treatment: “There’s no cure for color vision deficiency that’s passed down in families (inherited), but most people adjust to it.”
- Tinted glasses and contact lenses. The Institute says they “may help” by “increasing the contrast between colors so they’re easier to tell apart.” The American Optometric Association adds the limit: “nothing can make them truly see the deficient color.”
- Apps. The Institute notes that some apps let people photograph something and “tap on part of the photo to find out what color it is.”
- Acquired forms are a different matter, because the cause can be looked into. That starts with an eye doctor.
Designing for people with color vision deficiency
If you make charts, slides, maps or interfaces, the useful question is not “who is color blind?” but “does anything here depend on color alone?” A red line and a green line on the same chart can look identical to someone with protanopia or deuteranopia.
- 1
Run a screenshot through the Color Blindness Simulator. It applies a published model to show an approximation of protanopia, deuteranopia and tritanopia, on your own device, with nothing uploaded. It shows the strong form of each type; many people have a milder one.
- 2
Look for meaning that disappears. If two things became the same color, add a label, a pattern, a line style or a symbol.
- 3
Check contrast separately. Color and lightness are different things. The Color Contrast and Accessibility guide explains the WCAG rules, including the one that says color must never be the only signal.
The simulator is a design check, not a test. It says nothing about any person’s vision, and two people with the same diagnosis do not see identically.
Questions
Can ScreenTail test whether I am color blind?
No. ScreenTail does not offer a color vision test. The Color Blindness Simulator shows an approximation of how an image changes under three kinds of deficiency, which is useful for checking a design, but it says nothing about anyone's own vision. The National Eye Institute describes testing as something your eye doctor does.
Why is it so much more common in men?
The National Eye Institute puts it simply: "Men have a much higher risk than women for color vision deficiency." It adds that the blue-yellow and complete kinds "involve other chromosomes, so they affect people of different sexes equally."
Do color blindness glasses work?
They help some people. The National Eye Institute says special glasses and contact lenses "may help" by "increasing the contrast between colors so they're easier to tell apart." The American Optometric Association adds that "nothing can make them truly see the deficient color."
Can color vision change later in life?
Yes. The National Eye Institute says it "may also get worse as you get older — often because of cataracts", and that eye or brain diseases, injuries and some medicines can cause it. A change in color vision is a reason to see an eye doctor.
Is the screen I am using part of the problem?
It can be part of what you see. A screen that is too dim, set to a warm night mode, or badly calibrated changes colors for everyone. That is a question about the screen, not about your eyes, and it is covered in the How to Calibrate a Monitor guide.
How this guide was made
Every definition, figure and statement about testing and treatment is quoted from the National Eye Institute, MedlinePlus or the American Optometric Association (the American Academy of Ophthalmology's advice is summarized, not quoted), with the date each page was read. Where sources give different prevalence figures, the guide quotes each with the population it refers to. The description of the simulator is of ScreenTail's own tool.
No self-test of any kind, because a screen cannot present the colors of a clinical test reliably and the sources describe testing as an eye doctor's job. No advice on treatment beyond what the sources say, and no claim that any product works for any particular person.
- 01What color vision deficiency is, how common it is in men, what causes it, and that inherited forms have no cure but special lenses may help (page last updated November 5, 2025): National Eye Institute, Color Blindness — retrieved Sep 25, 2026.
- 02The types of red-green and blue-yellow deficiency, and complete color vision deficiency (last updated August 7, 2023): National Eye Institute, Types of Color Vision Deficiency — retrieved Sep 25, 2026.
- 03Inherited and acquired causes, including eye and brain diseases, some medicines and injuries (last updated January 30, 2025): National Eye Institute, Causes of Color Vision Deficiency — retrieved Sep 25, 2026.
- 04The color plate, anomaloscope and hue tests (last updated December 6, 2024): National Eye Institute, Testing for Color Vision Deficiency — retrieved Sep 25, 2026.
- 05Prevalence among populations with Northern European ancestry, and of blue-yellow defects worldwide (page last updated January 1, 2015): MedlinePlus Genetics, Color vision deficiency — retrieved Sep 25, 2026.
- 06Ishihara plates, and that the cards are held 14 inches (35 centimeters) from the face (review date January 20, 2025): MedlinePlus Medical Encyclopedia, Color vision test — retrieved Sep 25, 2026.
- 07Advice that anyone with a significant change in color perception should see an ophthalmologist (published July 2, 2026): American Academy of Ophthalmology, What Is Color Blindness? — retrieved Sep 25, 2026.
- 08That very few people are completely color blind, the share of men and women affected, pseudoisochromatic plates, and what tinted lenses can and cannot do: American Optometric Association, Color vision deficiency — retrieved Sep 25, 2026.
Try the tools
Not published yet, so not linked: Color Blindness Test.
Vivek Kumar runs ScreenTail from New Delhi. He has worked with computers for about 25 years and studied Computer Science. He is not a display engineer or a color scientist, and each guide says where its facts come from so you can check them.