LaGrange (Daniel Davis) asks why he would hire Sherlock (Jonny Lee Miller) if he was guilty. Sherlock says that he was once called in by a retired colourman (a dealer in colors and paints) to find his missing wife and lover, even though he had killed them. This was the plot of the 1926 short story "The Adventure of the Retired Colourman" by Sir Arthur Conan Doyle.
Daniel Davis played Professor Moriarty in two Star Trek: The Next Generation (1987) episodes: Ship in a Bottle (1993) and Elementary, Dear Data (1988) and one episode of Star Trek: Picard, The Bounty.
A foreign-trade zone, usually refers to a specially designated area considered outside the purview of United States Customs, subject to neither inspection nor import tax. Such a designation attracts a clientele of art smugglers, tax evaders and money launderers ( "Our clients have secrets. We offer discretion."). It was at one-time also known as a Freeport.
This episode's (7.3) guest star Gabriel Ebert and Elementary mainstay Jon Michael Hill had previously starred together off-Broadway in the play Pass Over (2018, at Lincoln Center's Claire Tow Theater). The pair were then reunited in the Summer of 2021 when they resumed their roles in Pass Over for the Broadway production at the August Wilson Theatre. Incidentally, Pass Over is the first play to open on Broadway (in August 2021) after over 17 months of the theatre shutdown due to the Coronavirus pandemic.
Even more, in the subsequent episode (episode 7.4 of Elementary), Namir Smallwood guest stars. He is the third member of the Pass Over off-Broadway and Broadway cast (alongside Ebert and Hill). The play itself only stars these three leading actors.