Color Blindness Test

How color vision works

Normal human color vision is trichromatic — it relies on three types of cone photoreceptors in the retina, each sensitive to different wavelengths of light. S-cones peak at ~420nm (short/blue), M-cones at ~530nm (medium/green), and L-cones at ~560nm (long/red). The brain combines signals from these three channels through opponent-process encoding: a red-green channel, a blue-yellow channel, and a light-dark channel.

Color perception emerges from the ratios of cone responses, not their absolute activation levels — which is why colors look roughly constant under different lighting conditions (color constancy). Deficiencies in one or more cone types alter how the brain encodes these ratios, making certain color pairs indistinguishable. This also explains why color blindness tests work by encoding numbers in hue contrast rather than lightness contrast — a person with normal trichromatic vision easily reads the number, while someone with a specific deficiency cannot distinguish the figure from its background.

Types of color blindness

The Ishihara test

Dr. Shinobu Ishihara of the Imperial University of Tokyo introduced his pseudoisochromatic plate test in 1917, initially to screen Japanese army recruits. Over a century later, it remains the most widely used color vision test worldwide — included in military entrance screenings, aviation medicals, and routine pediatric vision assessments in most countries.

Each Ishihara plate consists of a circular field of dots varying in color, size, and lightness. A number is embedded in dots of one hue against a background of dots in a confusable hue. Because the dots also vary in lightness and size, individuals cannot use brightness cues to identify the number — only chromatic contrast works. The 38-plate standard edition includes demonstration plates (visible to everyone), screening plates (missed by color-deficient individuals), and diagnostic plates that differentiate specific deficiency types. The version in this test is programmatically generated to approximate the chromatic contrast of the standard plates and serves as a preliminary screening only.

Who is affected? Genetics and prevalence

The most common forms of color blindness — red-green deficiencies caused by mutations in the OPN1LW (L-cone) and OPN1MW (M-cone) genes — are X-linked recessive traits. Because males have only one X chromosome, a single defective copy produces color blindness. Females have two X chromosomes, so both must carry the mutation — making female color blindness approximately 16 times less common than male. An estimated 8% of males and 0.5% of females of Northern European ancestry have some form of red-green color deficiency.

Living with color blindness

For most people, color blindness is a mild inconvenience rather than a disability. Common adaptations include relying on position cues (traffic lights are always red-top, green-bottom), choosing careers that do not require color discrimination, and using digital accessibility tools. Browser extensions like Chrome's Color Enhancer and apps like Colorblindness Simulator help both those with color blindness and designers who want to create accessible content.

EnChroma glasses use a notch filter to enhance chromatic contrast for people with red-green deficiencies. While they do not restore normal trichromatic vision, they can meaningfully improve color discrimination for individuals with anomalous trichromacy (protanomaly, deuteranomaly). They are less effective for dichromats (protanopia, deuteranopia) and do not help with blue-yellow or total color blindness. If you scored poorly on this screening, consider discussing a formal evaluation with an optometrist.

When to see an eye doctor

Congenital color blindness (present from birth) is stable throughout life and does not worsen or cause other vision problems. However, acquired color vision deficiency — color blindness that develops in adulthood — can be a sign of underlying conditions including glaucoma, macular degeneration, diabetic retinopathy, multiple sclerosis, or toxic reactions to medications such as hydroxychloroquine, ethambutol, or digoxin. If your color vision has changed noticeably in adulthood, this warrants prompt optometric evaluation.

Occupations with color vision standards — commercial aviation, electrical work, law enforcement, and certain military roles — require formal testing with calibrated Ishihara plates, Farnsworth D-15, or Nagel anomaloscope, not online screeners. This test can indicate whether further testing is warranted but cannot serve as a formal occupational screening. Always work with a qualified clinician for those determinations.