I rather like the idea of purple eyes. If the eyes were a very bluish purple I think they would make you look very carefully at the person. I bet it would be one of those things that just made a person more noticeable but that you might not necessarily put your finger immediately upon just what it was that made them remarkable.
I had a friend who had one of his eyebrows shaved off once by his buddies when he fell asleep after a night on the town. (Yes. The things boys do when they are young....) Anyway, the thing was it made him look ...interesting. Only slightly unusual. There was something different about his face but you didn't immediately notice what that was. I suppose our brains fill in the missing information if it is only a small missing piece. Things seem the same but there is an intuitive nagging that keeps you looking.
Sometimes we only see what we expect to see.