more on the shirts..

from Washington's Crossing, by David Hackett Fischer, published 2004, Oxford University Press, page 24:

Backcountry regiments from western Virginia were called "shirt men," from their homespun backcountry hunting shirts made of sturdy tow cloth that had been "steeped in a tan vat until it became the color of a dry leaf." Om woods or high grass they were nearly invisible. Congress recommended on November 4, 1775, that their hunting shirts and leggings be adopted for the entire army.