How does Mehendi colour skin?

Mehendi or henna leaves contain a colouring matter called lawsone. This is a dye which can bind with the protein in hair and nails. This protein is called keratin. The skin of the palms and soles also contain keratin, so the patterns drawn in mehendi show up well on palms. Mixing mehendi with indigo, logwood, coffee or any other natural plant colouring matter gives different tints.