Chroma

What it means

Chroma (Greek for “color”) is an old music-theory term for the chromatic alteration of a pitch by a half step using a sharp or flat. In medieval and Renaissance mensural notation, “chroma” also named a specially colored or shaped note used to indicate a different rhythmic value, a practice known as coloration.

In modern music theory and pitch perception, the term survives in a different sense: “chroma” now refers to pitch class, the quality a pitch shares across octaves (all pitches called “C” in any octave share the same chroma).

Musical use

Historically, then, chroma was both an accidental and, in mensural notation, a feature of the notehead itself. This older sense should be distinguished from the modern use of the word in pitch perception, where chroma and octave register (pitch height in the narrower sense) count as two separate dimensions of a tone.

Performance practice

If you meet the term “chroma” in a historical context, check whether it means an accidental or a special notehead; in a modern, analytical text it usually means pitch class without reference to octave.