Chroma
A color's saturation or clarity, from pure and bright to muted and greyed.
Chroma is the third of the three Munsell-derived dimensions used in seasonal color analysis, alongside hue and value, and it describes how saturated or muted a color is. A clear, fully saturated color like a pure primary is high chroma; the more grey is mixed into it, the lower its chroma becomes, until it reads as dusty or muted rather than bright. Munsell technically separates chroma, purity relative to a neutral grey of the same value, from saturation, but the two are used almost interchangeably in everyday color-analysis language. Chroma is the dominant characteristic behind four of the twelve seasons: Bright Spring and Bright Winter sit at the high, clear end, Soft Summer and Soft Autumn at the low, muted end. It is often the hardest dimension for beginners to judge, because a color can be objectively bright and still look soft simply because it is also light in value, or the reverse.
Why it matters
Chroma decides whether a flattering hue still flatters at full strength or needs to be softened. A Soft Summer and a Bright Winter can share nearly the same hue and value and still need completely different intensities of that color.