Henna!  The brilliant red dye that dyes skin. 

So, what is it?  Henna comes from a plant called Lawsonia Inermis.  It is mixed with lemon juice (and sometimes other ingredients in order to create a darker dye) and this paste is put onto the skin. This paste will leave a orange or red dye which will darken to a darker red (possibly even black, though that is unlikely) within 48 hours.  After this time it will begin to deteriorate.  A very good dye can last 3-4 weeks but others fade very quickly. Henna stains will vary depending on where on your skin the dye has been put.  Your palms and the soles of your feet will yield the darkest stains and will probably last almost longest (the best place for long lasting dye is your nails, the dye doesn't ever fade, merely grows out).

Whilst most henna designs only use one shade of red and create the pattern using outlines, shapes, detail and blocks of colour some designs will use shading or even add other colours through indigo, tumeric or other methods.