IMO, you can't reliably tell the difference. I have one of each side-by-side. One's a touch more violet with a hotter hot-spot, the other's a touch more greenish with a softer hot-spot. Not enough of a difference to warrant the extra $ to me, at least.
Oh - just re-read your first post: besides beam quality and pattern, I don't know of a way to tell the difference. (no super secret markings or anything that I'm aware of)