HEX vs RGB vs HSL
HEX (like #2546d1) packs red, green and blue into a
6-character base-16 string and is the most common format in CSS and
design tools. RGB expresses the same three channels as plain 0–255
numbers, which is easier to read when you're reasoning about individual
color components. HSL describes a color by hue (position on a color
wheel), saturation and lightness instead — often more intuitive for
picking a lighter or more muted version of a color, since you can adjust
lightness without changing the underlying hue.