Why "blue"?

Cursed a blue streak
Blue movies
etc.

Why “blue” to indicate offensive or risqué?

Etymologists are not sure why.

. . . but the most plausible theory is that is came from the term “bluestockings”, which was slang for England’s Puritans in the 17th century.

World Wide Words , Michael Quinion’s site is very professional. You can also read his take on it. But, Walloon is correct. Still undetermined.

Back in high school, my Spanish teacher told us that the Spanish equivalent is “es verde” (“is green”).

If this is true, why the color shift?

The Doppler effect?

Douglas Wilson, one of the “go-to” guys over at the American Dialect Society, found that green in Spanish to mean "obscene(or similar) is cited in the 1852 Royal Spanish dictionary.

Just adding more fuel to the fire.

May I add on: what about sad?

Feeling blue.
Got the blues.

Is it related?

Blue balls?

aaand…he runs off…

Want to know about other uses of “blue?”
http://alt-usage-english.org/concordance_interface.shtml

This is great site to bookmark. I think it’s listed in a sticky on board resources, but not everyone reads stickys. :mad