ON “The Marc and Myra Show,” on SiriusXM radio, the writer Bob Colacello recalled visiting Studio 54 in the 1970s when Yves Saint Laurent strolled into the room. Halston, on glimpsing his idol, sprang from his chair to embrace him. Taking in the scene, Truman Capote was heard to tell a companion: “You have just witnessed one of the great moments in the history of fashion. That is, if you care about the history of fashion.”