If you want an autoflower, I'd try to get some of Mossy's Purple AK-47...that bud was just like a purple crayon, dark waxy purple all over.
If you'll do a photoperiod strain, I'd recommend a pack of Cannabiogen's (or ACE) Purple Chitral Kush. I know there are green phenos in there, but as far as bag appeal, it's my favorite looking colored strain.
http://lmgtfy.com/?q=Purple+Chitral+Kush