Red Dun - dorsal stripe on a red dun horse. A red dun horse is a chestnut horse affected by the dun dilution. This dilution lightens the horse's body and gives it darker points and a dorsal stripe (a stripe down its back). Many duns also have shoulder stripes and zebra striping on their legs. A few also have cobwebbing on their foreheads, shadowing, and pale guard hairs.