Cards are handed out. An ace of diamonds is play placed on the table. Someone steals it. The magician asks multiple people if they have a red card or black cards the red cards...red ones have have to tell the truth the black ones have to lie and magi figures out who stole the diamond. Anyone know the name of this one? And where it's in print?

The one you are looking for is Pack of Lies in Karl Fulves Book - Self Working Close Up Card Magic. Page 20

Thanks Ferry - and I own that book too.

Really like those truth and liar plots, thanks for identifying it. Does this effect use a regular (ungaffed) deck?

@Mychine Yes just a regular deck and no set-up.

Great! Thanks for the confirmation - I will definitely look into it.