Different color models serve different purposes. HEX is the standard web format — every CSS color property accepts it. RGB describes color as red, green, and blue light values (how screens actually display color). HSL (Hue, Saturation, Lightness) is more intuitive for design — adjusting lightness or hue is straightforward compared to tweaking RGB channels.

Use cases: converting designer color specs to CSS, generating color palettes, checking WCAG contrast ratios for accessibility compliance, finding complementary/analogous colors for harmonious designs, and getting CSS-ready values to paste into stylesheets.