Color Blindness Simulator — Deuteranopia, Protanopia & Tritanopia

Color blindness (color vision deficiency, or CVD) is a condition where one or more types of cone cells in the retina are absent, non-functional, or respond differently to light wavelengths. The three types of cone cells are sensitive to short (blue), medium (green), and long (red) wavelengths. When one type is missing or altered, the ability to distinguish certain color combinations is reduced. About 8% of men and 0.5% of women of Northern European ancestry have some form of color blindness, with red-green deficiency being by far the most common.

Deuteranopia (no green-sensitive cones): the most common type, affecting ~5% of men. Red and green look similar, often both appearing as a muted yellow-brown. Protanopia (no red-sensitive cones): less common (~1% of men). Red appears very dark. Tritanopia (no blue-sensitive cones): very rare (<0.01%). Blue-yellow distinction is affected. Achromatopsia (no cone function): total color blindness — only brightness differences are perceived. Dichromacy (complete absence of one cone type) is the most severe form; anomalous trichromacy (shifted cone response) is milder but still causes difficulty with certain color pairs.

The simulator applies linear transformation matrices to the RGB color values based on the Brettel-Viénot-Mollon model (1997), the most widely cited scientific model for simulating dichromacy. First, RGB values are linearized (gamma removed). Then a 3×3 matrix representing the specific cone deficiency is applied to map the input color to the color seen by an affected viewer. Finally the result is gamma-encoded back to standard sRGB. The matrices are specific to each deficiency type and have been validated against experimental data from people with confirmed color vision deficiencies.

The core principle: never convey information through color alone. Always pair color with at least one other visual cue — a label, icon, pattern, shape, or position. For charts, use both color and pattern fill or direct labeling. For forms, use icons alongside error/success colors. For interactive states, use shape changes (border thickness, icon) in addition to color. Ensure sufficient luminance contrast (WCAG 4.5:1) between text and background — this helps both color blind users and everyone in poor lighting. Avoid the red-green combination for critical information since it's the most common deficiency pair.

Red and green are the most problematic — they appear nearly identical to users with deuteranopia and protanopia, which together affect around 6% of men. Pure red and brown, or orange and green, cause similar issues. Blue and purple can be confused by some users with general color vision issues. Red text on a black background can nearly disappear for protanopia users because red appears very dark. Using this simulator alongside our Contrast Checker gives you the most complete picture of how a color pair performs for accessibility across both contrast and color vision dimensions.

The most common forms of red-green color blindness are X-linked recessive traits — carried on the X chromosome. Since males have one X chromosome and females have two, a male with one affected X chromosome will be color blind, while a female needs both X chromosomes affected (making it much rarer). Tritanopia is autosomal and affects men and women equally. Achromatopsia is autosomal recessive. Acquired color vision deficiency can also result from eye diseases, aging, medication, or chemical exposure — it is not inherited in these cases.

Color blind-friendly palettes replace red-green combinations with alternatives that remain distinguishable under deuteranopia and protanopia. Well-known accessible palettes include the Wong 8-color palette (uses orange, sky blue, bluish green, yellow, blue, vermillion, reddish purple, and black) and the Okabe-Ito palette widely used in scientific data visualization. The key is choosing colors that differ in both hue AND luminance — two colors that are different hues but same luminance can still look identical to a color blind viewer. Our Color Analysis tool shows each color's luminance to help you build distinguishable pairs.

WCAG 1.4.1 (Use of Color) specifically requires that color is not the only visual means of conveying information, indicating an action, prompting a response, or distinguishing a visual element. This applies at WCAG Level A — the baseline. WCAG 1.4.3 (Contrast Minimum) and 1.4.6 (Enhanced Contrast) address the luminance contrast requirement, which also benefits color blind users. However, WCAG does not specify what colors to use or forbid any particular combination — it focuses on ensuring no information is conveyed by color alone and that contrast is sufficient.