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.

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

Munsell Notation

There 10 hues: R, YR, Y, GY, G, BG, B, PB, P, RP

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

5Y 8/10 and 5PB 4/20

There is a reasonable introduction to [1] in the Wikipedia.