Hmmm.... I'm guessing Mega Jirachi. I know it's out there, but look at it. The yellow for the 'wings' and the star head, the light greenish blue for the tassles, and the black for the eyes and inner eye line.
Niet also referred to the mega stone as a 'shinysparkle', which is similar to how the Jirachi at the Wishforge talks.
I noticed the similarity as well, and a Mega Jirachi would be totally awesome! I'll have to see if I can get a Jirachi from somewhere to evolve (if that's what the stone turns out to be).