"blue"(English)=obscene. Why "green" in Spanish?

[Barbara Need]

>A question from over at the Straight Dope.  I call on your help.
>
>We can all ascertain that "blue" was used in English since the
>1820's(and before) to mean "obscene."  See Michael Quinion's
>excellent write up at http://www.worldwidewords.org/qa/qa-blu2.htm
>
>A poster says that his Spanish teacher in High School told the class
>that in Spanish they use "green" to mean obscene.
>
>I can't offer more than that.  Is the poster correct about Spanish?
>If so, why the color difference?  When did it occur?
>
>Sam Clements

It is certainly green in Spanish, though I don't know why or when.

Barbara