Natural purple irises actually exist, but are extremely rare as they are the most recessive of iris colors.

I've never met anyone with purple irises. Amazing, nature is.

Naturally in a vial perhaps. Or some serious trauma to the eye.
Considering it's mostly melanin that deals with the colour of the eye and depending on the concentration it ranges from blue to grey to brown. Near or total absence leaves blood vessels more visible, leading to pink or red. Now that last one would be close, but to call it purple...

I suppose (read: guess) trauma to the iris could do it. Combining blue or grey blue eyes with some blood... I wouldn't want to bruise or even destroy my eyes over it though >.> Nor does it sound very hereditary if it's done that way.

Others species might get away with it. I don't know.

http://en.wikipedia.org/wiki/Eye_color

So that color actually exist for humans...just super rare?

EDIT:
Oh okay...well they have specific name colors other than what I said so I go by that link then.

I wouldn't mind having purple eyes as long as it wasn't caused by trauma ^^; Purple is one of my favorite colors~