Looking good!
I like the Palomino especially. :)

Do you think you could do something about the gray texture? Maybe it is the lighting in the render, but it just looks a bit like a black and white photo instead of a gray horse.
Maybe it's just because the colour of the mane and hairs is nearly the same grey. Most gray horses have darker hairs. But as you said you can combine different textures, that would be no problem. :)
http://thumbs.dreamstime.com/thumb_218/119759057959zl3D.jpg