Like 1fish2fish said, we may call them purple, but we've only ever gotten close once. I had my hopes dashed when I saw what I though was a purple female from local stock in my LFS, but I had to walk away in disgust after I saw she was blue with red-wash. (Nothing against the fish, but I hate red wash. Ruins otherwise great coloration.) It;s almost always some kind of wash that causes the coloration, and that's not always permanent.
I still hope one day we'll find the right mix that produces purple. =]