I'm by no means an expert so don't take this as 100%, but I have been told in the past that the true colour of henna has a dark green tinge to it. People add the black and brown to give it a more likable tattoo look which is where the problem begins and the costs come down. I would not be looking at getting a tattoo in bali but if you choose to and the colour is black or brown stay away. These additives to change the colour are toxic and that's why so many get a bad reaction.