HSL
Colour described as hue, saturation and lightness, close to how people talk about colour.
See it in Color palette. Pick a Base colour, then choose Analogous: its neighbours share saturation and lightness.
In plain words
RGB describes colour as amounts of light, which is hard to picture. HSL describes it with three plainer ideas. Hue is which colour, from 0 to 360 degrees. Saturation is how strong it is, and lightness is how light it is. To make a colour paler, you raise one number instead of changing all three.