I used the Lush caca (henna) about 3 times. I still have some left. Before applying the thing to my hair, I read carefully all the instructions on their forum and followed the outlined procedure.
Well, to my surprised, it was almost innocuous on my hair. I left the mix for at least 8 hours, and used the brun and rouge combined. Nothing but some very subtle cooper reflexes.
I wouldn't recommend this product, and I am a big fan of Lush. But it does work for a lot of ppl, so, you might give it a try. It comes on a bar with 6 squares, I had to use all of them to cover my hair.