This is going to make me sound like a purist, but I'd like to see some of the horse colours made more realistic. Yeah yeah, it's fantasy, /= realism, blah blah. My opinion differs - and if you're going to have horses, get the colours right.
Dark grey horses aren't common in any case, but to give them brown manes and tails and socks... ugh. Black, if you have to, which is actually remotely possible.
My Google-fu turned up
this interesting site on equine color genetics. (Yeah, I'm that retentive.
)
This one isn't bad either.
Saddlebag graphics would be nice, as a cherry on top rather than a requirement.
Many of the ideas above are sterling too!