“If someone tells you that a horse leapt to the bottom of an abyss without injuring himself, ask what color he was, and if you are told bay, then believe it. The bay says to an argument, ‘Come no closer!’” Arab proverb.
Of the dappled grey the Arabs say, “If he is like the stones in a river, he will refill the camp when it becomes empty, and he will save us in combat on the day when the firearms clash.”
Of the white horse the Arabs say: “This is the mount of kings, because he brings good fortune and luck…Take the white like a silk flag, with a ring of black skin around his eyes.”
The following are excerpts from http://www.touregypt.net/featurestories/arabianhorse.htm :
A bay horse has the best resistance in the extreme of temperature. They consider that he is better able to endure thirst, hunger, and, in fact, privations of any sort, than horses of other colours. A white horse is much esteemed, but to be a perfect specimen the muzzle, eyes and membranes must be black. The dark chestnut should gradually darken down the chest to the points so that all four legs are black; very often there is a deeper line in the dark chestnut with a medium line from the withers to the tail. Horses of this colour are highly prized. The black must have no light blemish; the muzzle must be absolutely black, as must be the colour round the eyes, nor should the coat of such an animal show a brown or reddish colour. The Arabs hold that black horses with red-rimmed eyes invariably get mad and vicious, and have a tendency to stampede, and in any case they are bad-tempered.
Briefly, the Arabs prefer:
The black horse.
The brown bay-with a star on the forehead and black mane.
The dark chestnut ( dark colours mean more blood ).
The white horse.
The black horse, being very rare and more full-blooded, was reserved for chiefs. A brown bay with a black mane is reputed to have a hard skin and good hooves, and greater endurance in extremes of temperature than the others. Great swiftness was attributed to chestnuts, as they always bore the first news of victories. The white horse is useful in hot countries, where the desert glare makes its detection by the enemy more difficult.
Markings that should be rejected are two trammels (white-foot) either diagonal or lateral, but two fore trammels or two hind trammels are acceptable; the latter are preferable to the former.
The white-legged horse is considered unlucky.
Castration of horses was forbidden by the Arabs, with the exception of thoroughly vicious animals.
A horse with bad teeth is of no value to the Arab, as he is considered incapable of feeding himself properly.
A horse's tongue must have no black lines, and the gums and palate must have no black spots on them.
Fidgety and noisy horses are considered useless, because they arouse the enemy.
The Arabs avoid thin horses because they say it is an indication of either disease or bad temper.
One must not have horses accustomed to drinking too often; such animals would be incapable of traveling long distances.