I just purchased LUSH henna and I can't seem to find anywhere online whether I should apply it to clean or dirty hair. I know with the henna I've been using, it needs to be on clean hair, but i don't know if there's a significant different with LUSH on clean or dirty hair. Has anyone tried it on both and seen a difference? I'd definitely prefer to do it on dirty hair because it's already such a long process that I don't want to have to wash it right before. But if i have to, i will. If it does need to be clean, does it need to be 100% dry or can it be damp?