Blue movie

Does anyone know the origin of the phrase 'blue movie'? I have found references to an Andy Warhol movie with the title "[f-word]" that was later changed to "blue movie" but was this the origin or was the phrase already in use by this time?

"Blue" for "obscene" dates back to the 1820s. See here: www.worldwidewords.org/ qa/qa-blu2.htm. And the Oxford English Dictionary has :
- 1959 Spectator 14 Aug. 180/1 "It meant that the theatre-going public were deprived of..outstanding contemporary plays, yet allowed to visit 'blue' variety shows."
- 1965 Punch 2 June 799/1 "He also wanted to see a blue movie."
This well pre-dates Warhol's film.
(VSD)