As I predicted when I linked to it, the very nice Games Workshop tutorial on painting horses has vanished from their website, which is a shame. Thankfully, there’s other good resources out there for horse colours and markings.
First of all, Wikipedia’s very useful article on Horse Markings has great diagrams of the variety of face, leg and body marks horses can have, and the Equine Coat Colourarticle, while not as nice as the markings one, at least has some good pictures of varieties of horse colour.
Veni Vidi Vici has some scans from an old children’s book of horses that nicely lays out the basic colours the beasts can have.
Steve Balagan has found some very nice photographs of horses to illustrate his Wargamers Guide to Horse Painting with, too.
All of this is, of course, in aid of me adding some 28mm cavalry to my Russian Civil War forces. More on that soon, I hope!