I've looked at all the kinds of floettes and the color flowers they could hold and AZ's Floette has a black flower. And also the actual Pokemon (not the flower) has black antenna things.
It's colors are very similar to Yveltal. Images have been appearing online of potential event Pokemon. AZ's floette being a common one. At this point I don't think anyone knows if it's shiny, I personally would guess it's just a special version of Floette. Here's a collection of a few images.