Every color on a screen can be described in multiple formats. #4f46e5, rgb(79, 70, 229), and hsl(243, 75%, 59%) are three ways of writing the exact same blue. They are different notations for the same underlying reality, like Celsius and Fahrenheit both describing temperature.
Hex: The Compact Standard
Hex codes (#RRGGBB) pack red, green, and blue channel values into six characters. They are the most common format in CSS, brand guidelines, and design tools. #4f46e5 means: 4f (79) red, 46 (70) green, e5 (229) blue. Compact, universal, but not human-readable (you cannot look at #4f46e5 and intuitively know it is blue).
RGB: The Machine Format
RGB (Red, Green, Blue) explicitly states the intensity of each light channel from 0 to 255. rgb(79, 70, 229) is more readable than hex if you know the system: high blue value (229) with low red and green means this is a blue. RGB is intuitive for adjusting individual channels.
HSL: The Human Format
HSL (Hue, Saturation, Lightness) describes color the way humans think about it. hsl(243, 75%, 59%) means: hue of 243 degrees (blue-violet region of the color wheel), 75% saturated (vivid, not muted), 59% light (medium brightness). HSL is the most intuitive format for making adjustments: want it lighter? Increase the L value. Less vivid? Decrease S.
Which to Use When
Use hex for storage and communication (brand guidelines, Figma specs, PaletteRx exports). Use HSL when you need to create variants (lighter, darker, more muted versions of a color). Use RGB when interacting with JavaScript canvas or SVG filters. PaletteRx shows all three formats for every color, so you always have the right notation available.