The Blood Runs Deep — Peter Taylor

Jim and Aaron were brothers. Jim was dark-skinned and Aaron was white, and this created a chasm between them that widened when Jim ran off to fight in the Civil War. After the war, and fleeing from the army and hostile Comanches, Jim rides into Texas seeking his mother. But soon the two brothers are united in pursuit of renegades and Red Bill, an adversary from Jim's war days… Jim and Aaron's relationship is tested. Does their shared blood count?