i have always wondered why no-one in that time period dyed there "new" off white shirts in blueberries, mulberries, or blackberries. the juice from these sure stain pretty well. did they not have any of these items back in the late 1700's?
Because you don't use food for dye, and none of those are very color-fast. They fade pretty quickly.
Poke-berries too.
Red and blue are tough to dye with natural dyes in North America, with Madder or Cochineal and Indigo being the preferred sources, Madder and Cochineal being imported, and Indigo being an intensive process.
Gray to black, yellow, light tan to dark brown, and even light green are available and simple veg dyes in North America. When I say simple, I mean that I was able to dye those colors.

I'm not very sophisticated in my domestic, cloth arts. An iron pot, boiling water, and some sort of plant is about all that I know.
If you check
http://etext.lib.virginia.edu/etcbin/ot2www-costa?specfile=/web/data/users/costa/costa.o2w you will find the differing colors available. Oznabrigs is an light brown, natural, course linen, and apparently very common in shirts and shifts.
LD