None of the sprays will work, actually. You'll end up with streaky, clumpy color that shows your natural hair right through the spray, and you will end up with flakes of that color on your shoulders and the rest of your costume.
Purple wigs in that style aren't all that rare and we can help you find one, but if you'd really prefer not to get one it's better for your hair and for the rest of your costume just to use your natural color.
ULTROS [Final Fantasy VI] (30%)
Haydee Tebelin (manga) [Gankutsuou] (10%)