Music-color synesthesia is the musician’s subtype of chromesthesia: the trigger is musical structure rather than raw sound. A key change moves the color of the whole passage; a chord has a blend distinct from its notes; one violinist’s tone differs in color from another’s.
Composers with the trait have used it structurally. Messiaen annotated chords with their colors and asked conductors for them; Scriabin built a color part into a symphony. Whether the trait steers people into music or simply gets noticed there more often is an open question.
Individual maps disagree with each other completely, which is why every attempt at a universal key-to-color chart has failed. The maps are real; they are just personal.