@invalid101 - yeah, I agree that the emerald's the closest.
Another possibility I guess would be buying the (http://arda-wigs.myshopify.com/collections/jasmine
) Jasmine in Mint and using a Sharpie? I've never Sharpie dyed before so I'm not sure if that would go too well. Maybe I'll just go with the emerald, considering in a lot of the artwork, Mion's hair is a lot darker than it is in the anime.
That is, assuming I ever get around to redoing this cosplay. Which I hope I do.