Yeah, I think there's a black platy in that jumble somewhere. Her face and part of her dorsal fins is jet black.
Something else I noticed that might or might not be important, you can't see it on the photos. When she faces the glass, the insides of her gills are actually white. it's definitely a marking, not some horrible fungus or what-not.
I can't believe I didn't grab her the absolute second I saw her. I'm in there all the time, every day I can I walk past the tanks and I go, wow, that's an attractive fish. But if I bought every wow, that's an attractive fish I would have overstocked the average swimming pool by now.
Next chance I get I'm going to see if there's any chance I can get more of those. If I could get a virgin and a male it would be ideal. I doubt it though, they always buy in a mix of colours. Platies aren't their best sellers, the more flashy tropicals do a much faster turnover, so there's not that much space dedicated to platies in there.
EDIT: Our TV is broken and tomorrow it goes to get fixed in a town about half an hour away. There's a pet shop there. You'd have to assume there would have been at least five or six of these in a drop so I'm going to see if any have turned up there. If there are some it might be a local supplier, which narrows down the possible origin of the cross a lot.