First of all, excellent, EXCELLENT job on the coloring and anatomy. This character looks supersolid, and very beautiful! Your choice of colors really works well, too, and the motion is very well-done.
I have some other notes, too. First of all, the wings look really pasted on, and pixely. If it were me doing this piece, I'd leave them off.
Second, you see how her black hoof just touches the front edge of her front leg? That's a tangent, and it makes it look like the black hoof is stuck to the leg. Either moving the hoof towards the rear more (so it looks like it overlaps the far leg) or pulling the hoof forward (so we see whitespace between the hoof and leg) will solve this problem.
I also notice in some places the character isn't entrely 3D. If you compare the chest, and the two legs, it doesn't look like the chest is very deep, which makes the front legs seem like paper cutouts. Showing the far back leg's knee also makes it look like her body has no roundness (instead of being like a sausage, it gives a feel of a paper cutout).
Finally, I'd like to see more structure on the face--especially the nose, which looks a tad flat.
Eh, I know that sounds like a lot, but it really isn't; just remember to think in 3D, and study up on horse faces a tad more.
Did I mention I like the shapes in the tail? Good stuff, man. You're an excellent artist!
AWW! This is so cute! I love the way you colored it and the anatomy. Realistic and yet not all at the same time.