That looks brilliant! I don't know if you are going for a more realistic look, but if you are what would take these to the next level would be possibly darkening the legs/muzzle, and trying out some cool patterns! They still look awesome though ❤️
I think the issue is that they look flat. When I do adopts, the horses never are just one color, they are a plethora of different tones and shades. As well as the hooves, they could use some more detail. Just widen your color palette.