 For all three tetrachords, only the middle two strings varied in their pitch.The term cromatico (Italian) was occasionally used in the Medieval and Renaissance periods to refer to the "coloration" (Latin "coloratio") of certain notes.The details vary widely by period and place, but generally the addition of a colour (often red) to an empty or filled head of a note, or the "colouring in" of an otherwise empty head of a note, shortens the duration of the note.