Munsell

Albert Munsell, Color Notation 1905

Munsell's color notation was the first to arrange the color perception components, hue, value, and chroma, into a three-dimensional arrangement. There 10 hues in Munsell's notation: R, YR, Y, GY, G, BG, B, PB, P, RP. Value ranges from 0 (black) to 10 (white). Chroma ranges from 0 (gray) to 30+. The hue is specified first, followed by value/chroma; e.g., 5R 3/4 is a red of value 3, chroma 4. There is a reasonable introduction to Munsell in the Wikipedia.

Hue, value, and chroma are all equal perceptual spacing!

5Y 8/10 and 5PB 4/20

Each hue goes from 0 to 10, e.g. 2.5RP; value goes from 0 to 10; and chroma goes from 0 to 30+