Body & Soul0 min ago
Horses
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For more on marking an answer as the "Best Answer", please visit our FAQ.Here in the western U.S., bay horses are generally medium brown in color. Most have black or darker brown stocking legs (usually on all four) and most have a black stipe down their spine, with a black mane and tail. Although it's primarily a color description, most bay's here are smaller horses. Roans, on the other hand, are reddish and somewhat dappled. That is, the reddish color is intermixed with a lighter color, often white. But the intermixing is much, much smaller that a paint horse. It also extends over most of their body, unlike Appaloosa's which tend towards blankets on the hips or more generalized spotting.
Here's a picture of a bay:
http://www.premierphotographer.com/horse_c74.html
While here's a picture of a roan (often called strawberry roan):
http://www.equusite.com/articles/basics/colors/colorsRoan.shtml
As you can see, there are great variations in each...
Sorry, can't help you with the war horse question...
To second Clanad's answer, a bay horse is brown with black mane and tail, and usually some degree on black on the lower legs.
A roan horse has white hairs spread throughout its coat - shades of roan vary according to what colour the rest of the coat hairs are. For example, a red roan is a chestnut coat with white hairs, and a blue roan is a black horse with white hairs.
This site give pictures! http://www.deannesweb.com/horses/horsecolors/colors/index.html
There are some sites referring to ancient horses:
http://www.humanist.de/rome/rts/horse.html
http://www.ancientworlds.net/aw/Journals/Journal/172694
http://members.ozemail.com.au/~ancientpersia/cavalry.html
Bay is a brown and can range from very dark brown (looks black, there are very few actual black horses) to to bright bay (almost ginger in colour, the difference between a 'ginger' bay and chestnut is that bays have black points i.e. main, tail and often lower legs.
Roans can come in different base colours as Noweia says, and can have bay as the base colour.