I've made my own shellac and I can't think of anything in it that would make a pipe green. Some shellac has a yellow tint. Of course, yellow and blue make green. I doubt your pipe was stained blue, but blue is used to make brown. So yellow plus brown could equal green. Who knows.
If the maker, manufacturer, is still active, or around you might try contacting them, of course there’s the chance the pipe had been stripped and redone which won’t get you a definitive answer.