χρῶμα

Khrōma is Greek, meaning skin, the surface color of the body, complexion. The word could also mean the color applied to a surface — paint, pigment, cosmetic. The connection between skin and color was literal: your khrōma was how your surface looked, the visible layer that covered everything beneath. Color was not abstract in Greek. It was the quality of surfaces, including the most intimate surface: your own.

Latin borrowed chroma for musical terminology. A chromatic scale includes all twelve semitones within an octave — the 'colored' notes that fill the gaps between the diatonic scale's white keys. The metaphor of color for musical variety dates to ancient Greek music theory, where the chromatic genus was one of three types of tetrachord, characterized by two intervals of a semitone. The colored scale was the one with more variety, more nuance, more detail between the main tones.

Modern color science uses chroma to mean the purity or intensity of a color — how saturated it is, how far it is from gray. In the Munsell color system, chroma is the axis that runs from neutral gray (chroma 0) to full saturation. A high-chroma red is vivid. A low-chroma red is muddy. The word that meant skin — the quality of a surface — now measures the intensity of that quality.

The prefix chromo- appears across English: chromosome (colored body), chromatic, monochrome, polychrome. In each case, the Greek word for skin and surface color underlies the modern scientific term. The most personal Greek word — the color of your own body — became the most impersonal prefix in the language of science.