Simulate how your colors appear to colorblind people. Test protanopia, deuteranopia, tritanopia and achromatopsia. Essential for web accessibility.
Protanopia (red) affects 1% of men — red becomes brown-green. Deuteranopia (green) is the most common (5% of men) — green and red are confused. Tritanopia (blue) is rare — blue and yellow are confused. Achromatopsia is the complete absence of color perception. These 4 simulations cover 99% of colorblindness cases to test for web accessibility.
To make your design accessible to colorblind users: never code information by color alone (also use shape, text, icon), ensure ≥ 4.5:1 contrast in grayscale, prefer 'colorblind-safe' palettes (blue/orange rather than red/green). WCAG 2.1 requires that color is not the only means of conveying information (criterion 1.4.1).