Sage tea for grey

I'm not gray yet, so haven't tried it, but your question peaked my interest.  I don't know if you've already read this article about it, but I found it the most informative article I'd read so far about what to expect and how to apply it (although I'd have to say the photos aren't that convincing)  http://www.newswriting.net/hair.htm
Since your hair has been dyed and is porous, I'd still test strand it to make sure it doesn't come out a strange color.