Home-made dye used to color "homespun" cloth a yellow-brown color, used when imported gray cloth became scarce.  The dye was made from the husks, leaves, bark, branches and/or roots of butternut and walnut trees.  "Butternut" was also a slang term for a Confederate soldier.

also butter-nut, 1753, nut of the white walnut, a North American tree; transferred to the tree itself from 1783. The nut's color was a brownish-gray, hence the word was used (1861) to describe th [..]

(n) North American walnut tree having light-brown wood and edible nuts; source of a light-brown dye(n) oily egg-shaped nut of an American tree of the walnut family