Munsell system

[Etymology: A. H. Munsell; USA 1858-1918] colorimetry A scheme for specifying the three components hue, chroma (saturation), and value of a colour, related to published samples but alphanumerically coded on a measured basis. Hue is coded from the capitalized initial letter of the labels red, yellow, green, blue, and purple arranged around a disc, singly interleaved with adjacent pairings. The numbers are prefixed with a number from 1 to 10 to show degree of gradation toward the next code, then onwards, e.g. 9 R, 10 R, 1 YR, 2 YR,…, 10 YR, 1 Y. This is followed by a number from 1 to 10 representing value then by a like number for chroma. The value is gauged from a series of equi-graded grey samples ranging from white to black by matching to the one equivalent in lightness. The chroma (saturation) represents the difference between these two matched items. The composite expression is punctuated as, e.g., 2 YR 4/6. The chroma is often seen as a radius, giving the Munsell wheel, with value expressed axially.
[Munsell A. H. A Color Notation (Baltimore MD: Munsell Color Co., 1936 onwards)]

Though introduced more for the arts, the Munsell system has been widely applied to science.
[Nickerson D. J. Opt. Soc. Amer. Vol. 30, 575-86 (1940)] Adjusted over time, mainly through re-scaling, it gave the Munsell renotation system,
[Newhall S. M., Nickerson D., Judd D. B. J. Opt. Soc. Amer. Vol. 33, 385-418 (1943)] and was a foundation for the ISCC-NBS system.