We had Yellow Book People when I worked at a deep discount bookstore a couple of decades ago. They were so named by the encounter of the Third Key* that I replaced.
Customer: "I'm looking for a book, I don't know the title or the author, but the cover is yellow."
Employee: "Let me take you to our yellow book section."
Customer: "You really have a yellow book section?"
Employee: "No, not really."
*Third Key was explained to me as "You'll be opening and closing the store some days, and you'll supervise other employees when the managers aren't around, if we ever get more employees."