Growing up in India, I always used henna for conditioning with an egg added to it. It didn't change the color of my black hair, but it gave it a reddish tinge when in the sun, which was a nice look.

Many people use henna as a natural dye. Soaking henna in black coffee or black tea has the effect you are looking for with coffee but adds to the conditioning of your hair. Look up good henna brands and if you wash and rinse it, you won't stain pillowcases.