How a color looks with protanopia, deuteranopia or tritanopia (red, green or blue color blindness), using the Machado et al. (2009) model.
Without green-sensitive (M) cones, #E74C3C is seen roughly as #9F8F36, a shift of 0.188 in OKLab distance. Don't rely on this hue alone to carry meaning; pair it with text, shape or a lightness difference.
Machado et al. severity-1.0 matrix, applied in linear RGB as colorspacious and DaltonLens do.
Channels are clipped to 0–1 before the sRGB curve and rounded half up to 8 bits.
The simulator converts the color from sRGB to linear light, multiplies it by the Machado, Oliveira and Fernandes (2009) matrix for the chosen type of color vision deficiency, clips each channel to the 0–1 range and converts back to sRGB. The severity 1.0 matrices used here model complete loss of the red-sensitive (protanopia), green-sensitive (deuteranopia) or blue-sensitive (tritanopia) cones. The color shift is the straight-line distance between the original and simulated colors in OKLab.
Designers use it to check whether a color still carries its meaning for people with color vision deficiency. The default red, #E74C3C, becomes the olive #9F8F36 with deuteranopia, a shift of 0.188 in OKLab, and #786D39 with protanopia.
The milder anomalous forms, such as deuteranomaly, are more common than the complete ones and shift colors less, so the simulation shows the strongest effect. Displays and viewing conditions also change how colors look.
Checked against: Separate Python 3.8 decimal script: sRGB → linear (IEC 61966-2-1), Machado 2009 severity-1.0 matrix, clamp, re-encode, round half up
Checked against: Separate Python 3.8 decimal script: first matrix column (0.152286, 0.114503, −0.003882) re-encoded; blue clamps to 0
Checked against: Each Machado matrix row sums to 1 within 1e-6, so linear (1, 1, 1) maps to itself (Python 3.8 row sums)
Checked against: Separate Python 3.8 decimal script: third matrix column (−0.178779, 0.147602, 0.303900) re-encoded; red clamps to 0
About 8% of men and 0.4% of women of European ancestry have red-green color deficiency, according to a 2012 review of population surveys by J. Birch in the Journal of the Optical Society of America A; among men of Chinese and Japanese ethnicity the figure is 4% to 6.5%. The US National Eye Institute puts it at about 1 in 12 men.
Each is the complete loss of one type of cone. Protanopia (no red-sensitive cones) and deuteranopia (no green-sensitive cones) make red and green impossible to tell apart. Tritanopia (no blue-sensitive cones) confuses blue with green, purple with red and yellow with pink, according to the US National Eye Institute. The milder forms, protanomaly, deuteranomaly and tritanomaly, shift colors less.
Deuteranomaly, reduced sensitivity of the green-sensitive cones that makes some greens look redder, is the most common type, according to the US National Eye Institute. Red-green deficiencies as a group are far more common than blue-yellow ones. This simulator shows deuteranopia, the complete form of the same deficiency, which is the strongest case of that confusion.
Don't use color as the only way to convey information. WCAG 2.2 success criterion 1.4.1, Use of Color (level A), requires another visual cue such as text, a pattern or an icon, and criterion 1.4.11, Non-text Contrast (level AA), asks for a 3:1 contrast ratio between interface components or graphics and the colors next to them. Check important color pairs here under all three types.
Accuracy depends on your inputs and the method's assumptions. Decimal arithmetic uses 50 significant digits, but estimates, numerical methods and source data can be less precise; the displayed rounding does not remove those limits. It is checked against 4 worked examples whose answers come from independent sources; for example, “Alizarin red with deuteranopia” is checked against Separate Python 3.8 decimal script: sRGB → linear (IEC 61966-2-1), Machado 2009 severity-1.0 matrix, clamp, re-encode, round half up.
Machado, Oliveira & Fernandes (2009), A Physiologically-based Model for Simulation of Color Vision Deficiency, IEEE TVCG 15(6):1291–1298; Machado et al. — simulation matrices for severities 0.1 to 1.0; DaltonLens — Understanding CVD simulation (matrices apply to linear RGB).
4 worked examples with independently sourced answers ship with this calculator. They run in the test suite; you can run them here too.
Check the WCAG 2.2 contrast ratio between a text color and its background, with AA and AAA pass or fail for normal text, large text and UI parts.
Convert a color from HEX to RGB, HSL, HSV, CMYK, CIE Lab and OKLCH or back, and find its nearest CSS named color and relative luminance.
Generate complementary, analogous, triadic, split-complementary, tetradic or monochromatic color palettes from one base color, with HEX codes.
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