Have you ever stained your shirt with tea (or coffee)?
It is exactly what it says - you dye your fabric with tea. (Can also be done with doffee)
Steep the tea to a dark reddish brown color and remove the bags then put the damp (prewashed) natural fiber fabric in the solution. Soak until the proper color is reached and rinse. Can be used to "antique" some bright fabrics. Works really well on muslin.