I actually prefer coffee to tea. It gives it a little different color that I like better. Take yesterday's leftover coffee and let is sit a few days to get really rank. Soak your cotton in it till it's a few shades darker than you want, remembering that it's going to lighten up once it dries. Let it dry to "set" the color, then soak it overnight in plain water to get rid of any excess.
Heck, I've got plain white shirts left from my executive days that have coffee stains persisting after years of my wife's best efforts with bleach and swear words.