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

[Sam Clements]

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