100 % wool can be dyed with tea. Though you might want to use superwash to dye the wool, just to avoid any felting that mght occur (though, if you're careful, no felting will happen).
What kind of method of dyeing do you want to use?
This seasons Knitty had a great article about dyeing yarn with non toxic methods. Instead of dye just use tea, but remember to keep the tea in the pouches.
And, remember, tea and coffee dye a lot softer than the dark colors you would assume.
I hope it turns out well though. Once I move into my new place (this Friday) and get setup, I'll put up a tutorial with LOTS of pictures, if that helps. I have some yarn that needs dyeing myself. :happydancing: