Thinking about using coffee or tea to stain fabric for your doll’s costume; maybe to tone down a too bright color or make it look older? They both work, and are ‘free’, but may eventually compromise your creation because of the acid. It is essential to dip the fabric and rinse, rinse, rinse some more to remove all trances of the coffee or tea.
An alternative to consider is using RIT dye (in the color Tan). The reasons are that it is made for dying fabrics so it works better, there is no acid to affect the fabric later on and does not cost very much. Just follow directions on the package.
Another tip: iron your fabric prior first. When a fabric has wrinkles they may absorb more stain or dye and leave streaks.