Roan

roan \ˈrōn, ˈrō-ən\ adjective: having the base color (as red, black or brown) muted and lightened by admixture of white hairs {a roan horse}
noun: 1. an animal (as a horse) with a roan coat (usually used of a red roan when unqualified), 2. the color of a roan horse (used especially when the base color is red)

Etymology: Middle French, from Old Spanish roano

Why do I get the feeling people use the word roan at renaissance fairs?