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. Data for conversion from Munsell to CIE XYZ can be found here. An online tool for exploring Munsell (unfortunately, Windows only) can be found here.

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+