Color vision deficiency (commonly called color blindness) affects approximately 8% of men and 0.5% of women worldwide. The most common types are deuteranopia and protanopia (both affecting red-green perception), followed by tritanopia (affecting blue-yellow perception). Designing without considering these users means your palette may be ambiguous or confusing for 1 in 12 male visitors.
The Red-Green Problem
The most critical design implication: red and green are the two most commonly confused colors, and they are also the two most commonly used semantic colors (error and success). If your only differentiation between "error" and "success" is red vs. green hue, users with deuteranopia literally cannot tell them apart.
Simulation Tools
Chrome DevTools includes a built-in color vision simulation: open DevTools, press Cmd/Ctrl+Shift+P, type "rendering," select "Emulate vision deficiencies," and choose from protanopia, deuteranopia, tritanopia, and achromatopsia. This applies a real-time filter to your entire page.
What to Look For
Run each CVD simulation and check: Can you still distinguish all interactive elements? Do error and success states still look different? Are chart colors and data categories still distinguishable? Can you identify which nav item is active? If any answer is "no," your palette needs adjustment for that state.
The Lightness Solution
The most reliable fix: ensure every color pair that carries different meaning also has a different lightness value. A dark red and a light green are distinguishable even without hue perception because the brightness difference survives all forms of color vision deficiency.