I just got a henna kit through the mail a few days ago - planning on trying it out this weekend!
And in the packet, there was even a warning about black henna - about how it is not true henna and that it can cause horrible allergic reactions.
I'll let you guys know how it works out - and if it goes well, I'll pass on the site I got it from, but I don't want to recommend it until I know for sure how well it works!