Billy Joel has discussed his synesthesia in interviews and in academic collections on the trait, describing melodies arriving with color: gentler, slower material in blues and greens, driving rhythmic material in reds, oranges, and golds. He has also described colors for vowels and letters, which points to a grapheme component alongside the musical one.
His accounts are notable for linking the colors to songwriting choices, using the color of a song in progress as information about what it wants to be.
Joel’s case is self-described and repeated across sources over many years, with the level of specific detail (which material goes with which color family) that casual list-articles usually lack.