Color Blindness Simulator

Color blindness, or color vision deficiency, is a condition where a person cannot perceive certain colors or cannot distinguish between colors that appear different to people with typical vision. It affects roughly 8 percent of men and 0.5 percent of women of Northern European descent, though the prevalence varies across different populations and ethnic groups. The most common forms are red-green deficiencies, which include Protanopia, Deuteranopia, Protanomaly, and Deuteranomaly. Blue-yellow deficiency (Tritanopia and Tritanomaly) and total color blindness (Achromatopsia) are significantly rarer. Most cases are inherited through a gene on the X chromosome, which explains why men are affected far more frequently than women. Acquired color vision deficiency can also develop later in life due to aging, certain medications, or eye and neurological conditions.

Protanopia and Deuteranopia are both forms of dichromacy that cause red-green color confusion, but they result from the loss of different photoreceptor types. Protanopia occurs when the L-cones (red-sensitive) are completely absent, causing the entire red end of the spectrum to appear dark and reducing the visible spectrum at the long-wavelength end. Deuteranopia occurs when the M-cones (green-sensitive) are absent. While both conditions make it difficult to distinguish reds from greens, Protanopia tends to make reds appear darker and more muted because the missing L-cones would normally respond to longer wavelengths. Deuteranopia shifts mid-spectrum colors but does not darken the red end as dramatically. In everyday life, both types cause similar challenges, such as confusing traffic light colors, difficulty reading color-coded information, and inability to see certain color contrasts in digital interfaces.

A color blindness simulator transforms input colors using mathematical matrices that model the effect of missing or altered cone photoreceptors. The process begins by converting the sRGB color value to linear RGB space using an inverse gamma function, because color operations must be performed on linear values to produce physically accurate results. Next, the simulator applies a 3x3 color transformation matrix specific to each type of color vision deficiency. These matrices are derived from the Brettel, Vienot, and Mollon research, which characterized how the human visual system processes color signals when one or more cone types are absent or abnormal. After the matrix multiplication, the resulting linear RGB values are converted back to sRGB with gamma encoding. The anomalous trichromacy types (Protanomaly, Deuteranomaly, Tritanomaly) use a blend between the normal and dichromatic matrices, reflecting the partial rather than complete loss of cone function.

Tritanopia is a blue-yellow color vision deficiency caused by the complete absence of S-cones (short-wavelength or blue-sensitive photoreceptors). Unlike Protanopia and Deuteranopia, which affect the ability to distinguish between red and green hues, Tritanopia impairs the ability to distinguish between blue and yellow, and between blue and green. People with Tritanopia typically perceive the world in shades of pink and teal. It is extremely rare, affecting fewer than 1 in 10,000 people. Another important distinction is that Tritanopia is not sex-linked; the gene responsible is on chromosome 7 rather than the X chromosome, so it occurs at roughly equal rates in men and women. Designers should be aware of Tritanopia when using blue-based color schemes or blue-yellow contrasts, as these combinations may be indistinguishable to affected users.

The Web Content Accessibility Guidelines (WCAG) specify minimum contrast ratios between text and its background to ensure readability. WCAG 2.1 Level AA requires a contrast ratio of at least 4.5:1 for normal text (below 18 point or below 14 point bold) and 3:1 for large text (18 point and above, or 14 point bold and above). Level AAA raises the bar to 7:1 for normal text and 4.5:1 for large text. The contrast ratio is calculated from the relative luminance of the two colors using the formula (L1 + 0.05) / (L2 + 0.05), where L1 is the lighter color's luminance and L2 is the darker. These requirements apply to both body text and user interface components like buttons and form labels. Non-text elements such as icons and graphical objects require a minimum 3:1 contrast against adjacent colors under WCAG 2.1 Success Criterion 1.4.11.

The most important principle is to never use color as the only means of conveying information. Pair color indicators with text labels, icons, patterns, or shape differences so that meaning is preserved for users who cannot perceive the color difference. For example, use a checkmark icon with green for success and a cross icon with red for errors, rather than relying on color alone. Choose a color palette that maintains distinguishability across common types of color vision deficiency by testing it with a simulator. Blue and orange are generally safe contrasting colors because they remain distinct for most forms of color blindness. Ensure all text meets WCAG contrast ratio requirements against its background. Use underlines or other non-color indicators for hyperlinks. In charts and data visualizations, add direct labels or use textures and patterns in addition to color coding.

Achromatopsia, also known as rod monochromacy or total color blindness, is a condition in which none of the cone photoreceptors function. People with Achromatopsia perceive the world entirely in shades of gray and have no color vision at all. It is extremely rare, estimated to affect between 1 in 30,000 and 1 in 50,000 people worldwide, though it is more prevalent in certain isolated populations such as the island of Pingelap in Micronesia. In addition to the complete loss of color perception, Achromatopsia typically causes extreme sensitivity to light (photophobia), significantly reduced visual acuity (often 20/200 or worse), and involuntary rhythmic eye movements called nystagmus. Achromatomaly is a milder variant where some residual cone function exists, allowing for severely limited but not entirely absent color discrimination.