HEX / RGB / HSL
Three ways to name the same color.
Where it came from
Screens mix red, green and blue light, so RGB is the native model: three 0–255 intensities. Hex is just RGB written in base-16 for compactness in code. HSL (Hue, Saturation, Lightness) came later as the designer-friendly view.
CSS supports all three; pick Hex for copy-paste, RGB for clarity, HSL when you want "a lighter shade of this hue" without math.
How it works
RGB(r,g,b) names the three channels directly. HEX collapses them to #rrggbb. HSL describes a color by hue angle (0–360), saturation and lightness — intuitive to tweak.
Conversion is fixed math: HSL→RGB→HEX are pure functions. UWC converts any of the three to the others in your browser, ideal for quick theming.