Wow, I absolutely love this piece, because it is quite intriguing.. You did a magnificent job! The mane and tail look perfect, along with the lighting. The colors in this all tie in together - which is what I have a problem with myself. The only thing I think looks a bit strange - are the back legs and hoofs. I don't know why but they seem a little off to me. However, this piece is better than anything I could ever do and I am in love with it. <3 Let me just say one more thing - WOW JUST WOW!
Something that has already been pointed out, is those back hooves. It is as if the horses joints there are rubber, and it just stands out way too much. You flipped the legs around, if you look back at the stock you used.
Next would be the shadow. Its like you just duplicated the horse, flipped is and changed the opacity. You haven't taken into consideration the grass.For example, the long grass near the front hoof touching the ground, that would be in front of the shadow, and would be overlaying it. Then t=in the water, it would be a little more blurred, due to the motion in the water. And would also be a "reflection" more then a shadow.
I have to say, the background is very distracting from the main subject. The blurriness of it blends the horse in a little too much. With some people, they do this to "Bring" attention to the subject. But i think in this particular piece, its either "Too" blurred, or just isn't the right thing for the particular placements.
With your lightning, a little hint. Try re painting some brighter hi lights on it, and some lose strays which wrap around it. Giving it a little more realism too it. As at the moment, the lightning blends into the blurriness of the back.
Now that the mean stuff is over (The bit i hate about giving crits) i can congratulate you on a PERFECT colour change on the horse. I myself have difficulties on colour changes, but you pulled it off perfectly!
Then that necklace charm. Its amazing, not sure if you fully painted it or not, but still looks lovely!