If you're going to henna, get the BAQ mehndi kind instead. I've used both and found the Lush henna bars really lacking — less color, hard to apply, etc. I also found that it faded, which real henna does not do. And it didn't fade in a good way, if that makes any sense.
It's kind of unusual for me to dislike one of Lush's products, actually. I usually love their stuff.
I cannot speak to the caca noir, marron, brun … just the caca rouge, which is no match for BAQ henna.