CSS supports multiple ways to write the same color. #4f46e5 (hex), rgb(79, 70, 229) (RGB), and hsl(243, 75%, 59%) (HSL) all produce the same blue. Each format has practical strengths.
Hex (#RRGGBB)
Hex is the most compact and widely recognized format. Six characters encode red, green, and blue channels as pairs of hexadecimal digits (00 to FF). It is the lingua franca of web color: every tool, every framework, and every designer understands hex. PaletteRx uses hex as its primary format because of this universality.
RGB (Red, Green, Blue)
RGB expresses the same channels as decimal numbers (0 to 255). It is more readable than hex for people who think in terms of channel values. rgb(79, 70, 229) is immediately understandable as "low red, low green, high blue." RGB also supports an alpha channel: rgba(79, 70, 229, 0.5) for 50% opacity.
HSL (Hue, Saturation, Lightness)
HSL describes color the way humans think about it: hue (the color, 0 to 360 degrees on the wheel), saturation (how vivid, 0% to 100%), and lightness (how light or dark, 0% to 100%). HSL makes it easy to create shade scales: keep hue and saturation constant, vary lightness. It also makes relationships visible: two colors with the same hue are tints of each other.
When to Use Each
Use hex for storage, communication, and configuration (most tools and frameworks expect it). Use HSL when you need to create shade variations or understand color relationships. Use RGB when you need alpha transparency in older CSS. Modern CSS also supports hsl() with alpha: hsl(243 75% 59% / 50%).