Henna is a type of plant with a natural staining ability. If you touch the leaves of the plant, it will stain your skin a beautiful reddish brown color. The leaves are ground into a powder, the powder is mixed with a natural oil to turn it into a paste, and a henna artist can draw with that paste in a controlled manner on the skin. The stain will happen wherever the paste touches your skin. If your henna artist offers anything other than that reddish brown color, then there’s something else in their mixture to change the color!
Remember that the paste is green when the artist begins drawing. It’s made from a plant, after all. The green is going to darken as the paste dries in about 20 minutes so that the paste will look blackish by the time it is dry. The dried paste crumbles and falls away. The stain that is left behind will look lighter in color the first day appearing yellow/orange. That will darken over about 24 hours, and the next day the stain will be a beautiful reddish brown color. That color sticks around for a few weeks to enjoy before it fades away.
Be smart, be savy, and do your research before putting anything on your skin. Henna paste should have all natural ingredients. So ask your henna artist what is in their mixture so that you can comfortably enjoy your henna tattoo experience!