coffee hair stain?

[emmaya]

I read that you can use coffee to "stain" your hair...doesn't the acid hurt it?
or do you oil up before/during?
How long to leave it in?
how frequently to keep up the results? (I don't mind my grays, but after years of texas sun, my ends are MUCH lighter than my roots, and I like the darker color!)

[skyblue]

I'd be interested in knowing this too....I hate wasting coffee I would much rather put it to good use then pour it down the drain ;)