@Robbo, “turning the air blue” does indeed refer to swearing.
When comedians refer to “working blue” or “blue material”, they’re talking about the X-rated routines like you’d find on old “stag” or “party” LPs, with dirty jokes and lots of strong language. Rusty Warren, Ruth Wallis, Redd Foxx, Lenny Bruce, Mae West… all masters of the blue.
Too bad blue material is so mainstream nowadays that it’s become boring.
http://www.youtube.com/watch?v=hHgl762qGso
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