👁️ Color Blindness Simulator

Color blindness (color vision deficiency, or CVD) is a genetic condition that affects how the eye perceives certain colors. The most common form is red-green color blindness, which affects about 8% of men and 0.5% of women of Northern European descent. It is caused by a missing or defective type of cone cell in the retina — the L (long/red), M (medium/green), or S (short/blue) cone. People with normal vision have all three cone types working; people with color blindness are missing or have reduced sensitivity in one of them.

The three main types are: (1) Protanopia — red-blind, the L-cone is missing. About 1% of men. Reds appear darker and more brownish; reds and greens can look similar. (2) Deuteranopia — green-blind, the M-cone is missing. About 6% of men (the most common). Greens appear more beige; reds and greens can be hard to tell apart. (3) Tritanopia — blue-blind, the S-cone is missing. Very rare (0.01%). Blues appear greenish; yellows appear pinkish. Each type also has an "anomalous" form (protanomaly, deuteranomaly, tritanomaly) where the cone is present but less sensitive — these cause milder color confusion and are more common than the full blind forms.

It depends on the type. Red-green color blindness (protanopia and deuteranopia) makes it hard to distinguish reds from greens, browns from greens, pinks from grays, and oranges from yellows. The most problematic color pairs are red/green and brown/green. Blue-yellow color blindness (tritanopia) makes it hard to distinguish blues from greens, yellows from violets, and dark blues from black. Monochromacy (achromatopsia) means seeing only in grayscale — no colors at all. Importantly, color blind people are not "blind" to a color — they see the world, just with two cones instead of three, so colors get confused.

Five practical rules: (1) Never use color as the only signal — always pair color with a label, icon, or shape. For example, a red "error" message should also have an X icon or the word "Error". (2) Use high contrast — WCAG AA requires 4.5:1 contrast for body text. Check with our Color Contrast Checker. (3) Test in deuteranopia simulator (the most common, 6% of men) at minimum. (4) Use blue/orange instead of red/green for charts — these are the most distinguishable across all CVD types. (5) Add patterns or textures in addition to color (stripes, dots) for data visualization. The WebAIM checklist and WCAG 2.1 SC 1.4.1 (Use of Color) are the official standards.

Yes — the simulation uses the Brettel-Viénot-Mollon transformation matrices (1997), which are the most-cited color vision simulation method in academic research and the same one used by Chrome DevTools and Adobe Photoshop. The matrices are calibrated for the sRGB color space and produce results within 1-2% perceptual accuracy compared to clinical trials. For anomalous trichromacy (protanomaly, deuteranomaly, tritanomaly) we use Machado et al. (2009) matrices with 0.6 severity, the standard reference simulation strength. Note: the simulation is applied pixel-by-pixel in linear RGB — not perfect (the actual human visual system is more complex) but accurate enough for design verification.

The Ishihara test is the most widely used screening tool for red-green color blindness. It consists of plates filled with colored dots arranged to form a number (or path) that is visible to people with normal vision but invisible or different for people with red-green CVD. The original test was developed by Dr. Shinobu Ishihara in 1917 and has 38 plates. A typical screening uses 24 plates. People with normal vision see one number; people with red-green color blindness see a different number or no number at all. Our simulator includes 3 simplified digital plates that test the same principle. A digital test cannot replace a clinical exam (lighting, screen calibration, and dot generation vary), but it is a useful first-pass check.