All natural (mostly) wood stains! A handful of pennies in vinegar will produce a beautiful pale Caribbean blue stain. A wad of steel wool will give you a rich reddish hue. A combination of tea and a metal object in vinegar will produce a black stain.
Stain recipe - 1 cup vinegar (Either white or apple. Apple produces a little more of a teal color rather than bright blue.) - cup hydrogen peroxide - 40 ish pennies (this number varies largely on the amount of tint you want to your vinegar.