Why AA and AAA matter: WCAG 2.1's contrast guidelines exist so text stays readable for people with low vision, color blindness, or when reading on a low-quality/glare-affected screen. AA (ratio ≥ 4.5:1 for normal text, ≥ 3:1 for large text) is the widely-adopted legal minimum in many accessibility regulations. AAA (≥ 7:1 / ≥ 4.5:1) is a stricter, "enhanced" target recommended for content where readability is critical.