blue movie

[MrRuss]

Where did the term "blue movie" come from?

[Quizmonster]

Blue laws were those set by Puritans in America in the 17th century, generally forbidding anything resembling enjoyment - particularly on the Sabbath - and seemingly published on blue paper.
In addition, the censor of British plays - someone appointed by the Lord Chamberlain - had to vet theatrical and, later, film-scripts with a view to cutting out anything obscene. He would score through any offending words with a blue-coloured pencil.
So, 'blue' in general took on the meaning of 'smutty' and hence the application of that adjective to the sort of films you refer to.

[Mr Songman]

And here's the rest of that article:

" While there's no proven connection between these uses of "blue," it's not inconceivable that both influenced the term "blue movies." Pornography has been outlawed at various times and places, so blue laws might have forbidden the movies and thus the color became associated with the content. Also, when you curse a blue streak, you're talking dirty, and such language can be connected to explicit films. Another explanation for "blue movies" is that striptease acts may have once used blue spotlights. "

The use of the word "blue" to refer to risqu� content was first recorded in Scotland in 1824

" What we do know is that the word began to be applied to matters obscene in the 1820s. (There�s an entry for it in The Scottish Gallovidian Encyclopedia by John MacTaggart of 1824: �Thread o� Blue, any little smutty touch in song-singing, chatting, or piece of writing�).

So it long pre-dates, for example, any reference to or the use of editorial blue pencils to delete anything suggestive, which seems to be a late nineteenth-century joke based on the pornography, by then well established."

Yet another is that it comes from brothels in pre revolutionary China which were painted blue outside to advertise the presence of prostitutes within!

So not quite so straightforward after all!!