Color Blind Test (Free Online Screening)

How this color blind test works

The test has two parts. In Part 1 you see 10 circular plates filled with dots of different sizes and lightness, each hiding a number. Tap the number you see, or I can’t see a number if you see none — don’t guess. In Part 2 you start from a reference color (★) and line up similar colors one after another. The two parts together point to possible red-green or blue-yellow color vision deficiency.

The plates are not copies of Ishihara plates. A new set is generated every time you start, with new dot layouts and numbers, so answers can’t be memorized and you can retake the test to check that your results are consistent.

• 2 control plates: designed with a large lightness difference so everyone can read them. Missing one usually means a screen setting or misunderstanding, so the result is marked inconclusive.
• 6 red-green plates: colors on the protan and deutan confusion lines, each at strong, medium and faint strength.
• 2 blue-yellow plates: colors on the tritan confusion line at strong and medium strength.

Tips for an accurate result

A screen-based test depends heavily on the screen itself. These steps make your result far more trustworthy.

• Turn off night mode and blue light filters (Night Shift, Night Light, Eye Comfort and similar). They tint the screen yellow and can hide the blue-yellow plates in particular.
• Temporarily turn off accessibility settings such as color filters, grayscale and color inversion.
• Raise the screen brightness and use a bright room with white light, not colored mood lighting.
• Remove color-enhancing glasses and tinted sunglasses. Keep your normal prescription glasses on.
• Don’t stare at a plate for a long time; clinical plate tests also ask for an answer within a few seconds.
• If you can, repeat the test on a second device. Missing the same plates on two screens makes a screen problem less likely.

Understanding protan, deutan and tritan results

Your retina has three kinds of cone cells, sensitive to long (L, reddish), medium (M, greenish) and short (S, bluish) wavelengths. When one type is missing or shifted, some colors become hard to tell apart. Colors that look identical to a given type of observer lie on straight “confusion lines” in a chromaticity diagram that meet at a single point. The plates in this test draw the number and the background from the same confusion line.

• Protan (L cones affected): reds, greens and browns are confused, and reds look darker than they do to others.
• Deutan (M cones affected): the most common type; greens, reds and yellows are confused.
• Tritan (S cones affected): blues and greens, yellows and violets are confused. Inherited tritan deficiency is rare.
• Dichromacy vs. anomalous trichromacy: when one cone type is essentially absent, it’s called dichromacy (protanopia, deuteranopia, tritanopia); when it is present but shifted, it’s anomalous trichromacy (protanomaly, deuteranomaly, tritanomaly). Missing even the strong plates points toward dichromacy; missing only medium or faint plates points toward a milder form.

How common is color blindness?

According to the U.S. National Eye Institute (NEI), about 1 in 12 men have a color vision deficiency, and red-green deficiency is by far the most common type. Korea’s national health information portal reports about 5.9% of men and 0.4% of women.

Genes for red-green deficiency are carried on the X chromosome. Men have one X chromosome, so a single affected gene is enough; women need the gene on both. Blue-yellow deficiency involves other chromosomes and affects men and women equally.

Color vision can also change later in life. NEI lists eye diseases such as glaucoma and age-related macular degeneration, brain and nervous system diseases such as Alzheimer’s and multiple sclerosis, some medicines (for example Plaquenil, used for rheumatoid arthritis) and injuries such as retinal detachment. If colors you used to tell apart start looking alike, see an eye doctor regardless of what this test says.

How we built this test (sources)

The dot plates follow the approach of the Cambridge Colour Test described by Regan, Reffin and Mollon (1994, Vision Research 34). The number and background are placed on confusion lines in the CIE 1976 u′v′ diagram, using the copunctal points from that paper (protan x=0.747, y=0.253; deutan x=1.40, y=−0.40; tritan x=0.171, y=0), and every dot gets one of six random lightness levels so the number can’t be found by lightness alone — a principle that goes back to the ophthalmologist Stilling’s plates of the 1870s. We also set the number’s lightness so that the remaining cone signals of the matching observer type (using the Smith & Pokorny 1975 cone fundamentals) are equal, so the number and background look equally light to that observer.

The arrangement task is our own implementation inspired by the clinical Farnsworth D-15 test. Sixteen colors of equal lightness and chroma sit 20° apart on a CIELUV hue circle, and the result is scored with the color-difference vector method of Vingrys and King-Smith (1988, Investigative Ophthalmology & Visual Science 29), which yields a confusion angle, a confusion index (C) and a selectivity index (S). The simulated views use a simplified version of the dichromat simulation by Viénot, Brettel and Mollon (1999).

All calculations assume a standard sRGB screen. Real screens vary, which is why this test can only support screening, never diagnosis.

What to do if your result worries you

An eye care professional can diagnose color vision deficiency with standardized plates under controlled lighting, arrangement tests and, in some clinics, an anomaloscope that measures the type and severity precisely. If a school, job or license has color vision requirements, check that organization’s standard and testing method first.

There is no cure for inherited color vision deficiency, but most people adapt well. Phone accessibility settings such as Color Filters on iPhone and Color correction on Android can make colors on screen easier to tell apart. NEI notes that special glasses and contact lenses may help some people tell colors apart, but they don’t restore normal color vision.