Chromatic scales use sharps and flats (accidentals) to cover all the notes. (With only eight letter-names, and twelve tones, some notes do double-duty.) “Accidentals” are sharp, flat and natural symbols not in the key of the piece. They’re notated in-line on the sheet music, instead of at the beginning of each line. When we see a cluster of accidentals, we can guess that there’s a chromatic scale at work.