 Rocky Mountain Horses stand between 14 @.@ 2 and 16 hands ( 58 and 64 inches , 147 and 163 cm ) high . Any solid color is accepted by the registry , but a dark brown color called " chocolate " with a pale , " flaxen " mane and tail is preferred . This coloration is the result of the relatively rare silver dapple gene acting on a black base coat . Although uncommon , this gene has been found in over a dozen breeds , including the Rocky Mountain Horse . <unk> white markings are accepted by the registry , although leg markings may not extend above the knee . The physical characteristics are somewhat variable , due to the disparate breeds that created the Rocky Mountain Horse . The Rocky Mountain Horse is known by enthusiasts for its <unk> and ability to withstand winters in the mountains . It is also praised for its good nature and affinity for humans . Rocky Mountain Horses have the highest risk of any breed for the genetic ocular syndrome multiple congenital ocular <unk> ( MCOA ) , originally called <unk> anterior segment <unk> ( <unk> ) . MCOA is characterized by the abnormal development of some ocular tissues , which causes compromised vision , although generally of a mild form ; the disease is non @-@ progressive . Genetic studies have shown that the disorder may be tied to the silver dapple gene , as most horses diagnosed with MCOA carry the gene . 
