Sherlock tells Marcus that purple is not one of the colors women are attracted to; in the other modern Sherlock Holmes adaptation airing concurrently on the BBC, their version of Sherlock famously wears a (tight) purple shirt dubbed "the purple shirt of sex" by the fans.
Last episode, Sherlock mentioned the "Codex Seraphinianus" (a book whose author is named Serafini). This time he mentions a character named Serafina di Tomasso.