A friend of mine bought the yellow cat eye lenses for a halloween costume, and the pupil-hole is really small, you can only see the color of your eyes if you have really bright light pointed right at your eye(which make your pupil really tiny). But the only problem though, is that the lenses turn sideways, which makes you look like a goat instead of a cat.. But I don't think it's possible to find lenses that does not move in your eye anyway.
As for purple lenses I have no clue..
I would suggest these
red ones. They have a natural yet really strong look and the color shows up really good, even on dark eyes.