Denzel Washington and Wesley Snipes were trained to mimic the playing of the instruments they play in the film (trumpet and saxophone), by musicians Terence Blanchard and Donald Harrison. Washington later admitted that he was lucky if he could play three notes of a simple tune prior to filming, and ended up being able to correctly mimic most of the songs performed in the film, along with Snipes.
Wesley Snipes' character, Shadow, purchases a stack of John Coltrane CD's with an American Express card. When he shows his American Express card he smiles and says: "American Express. Gold card, pow. Been a member since 1989". In 1989, Snipes had another encounter with the American Express credit card, in the movie Major League (1989). Snipes' character, Willie Hayes, acts in a commercial for American Express in which he slides into home saying "American Express, don't steal home without it".
At roughly 28:37 into the film, there is a sign from a club that reads, "Underneath the Underdog". This is a reference to the great Jazz Bassist and composer Charles Mingus and his autobiography of the same name.