Ritenne che la maggior parte dei pendolari aveva una grande passione per i racconti gialli.
She found that the majority of commuters had a great passion for yellow [detective] stories.
Captions 36-37, L'Eredità -Quiz TV - La sfida dei sei. Puntata 2Play Caption
Here, although the color yellow does play an important role, un giallo is something specific: a crime, mystery or detective story. Note: The moderator of the quiz show uses giallo as an adjective: i racconti gialli (the detective stories) and it is common to say un romanzo giallo (a detective novel), to specify the format, but giallo as a noun encompasses any format and is widely used and understood by Italians.
But what's this "yellow" business?
Here's the story. (click here for the extended Italian version).
In 1929, Mondadori, a major Italian publishing house, came out with a series of detective novels. They were tascabili (in paperback, literally "pocket-sized") and had a distinguishing yellow cover. They were called I libri gialli della Mondadori (Mondadori's Yellow Books). In 1946, the name of these books changed to I gialli Mondadori. The name giallo caught on, and has been used ever since to indicate a detective, crime, or police mystery, and can be applied to books, comic books (as in Diabolik mentioned on the quiz show), movies, or even news events. Giallo with this meaning has become a word everyone should know, especially if you like to read. And it can't be guessed at if you don't know the story. But now you know the story, too.
You may have heard of an American television series from the eighties and nineties called Murder, She Wrote with Angela Lansbury. This series, dubbed into Italian, became extremely popular (and stilll is) as La Signora in Giallo (The Lady in Yellow). This play on words should make sense to you now!
Read this article (in Italian) for more information about the Italian version of the show, and, why not? Find it for streaming in Italian, just for fun.