The henna on the back of hand and down the arm is deep chocolate color; the fingertip and palm henna is ripe blackberry-black.  No dyes or colorants other than natural henna were used.  No wrap was used. No steam was used. Cajeput essential oil strongly reacts with the henna molecule, resulting in very dark stains with no added heat or wrap. 

Technique:
Plain bulk henna powder from Castle Art, http://www.castleart.com, mixed with lemon juice and left for 10 hours, then 1/2 tsp Cajeput essential oil added to 2 tbsp of paste.  The paste was allowed to sit a further 12 hours.  Paste applied, dried, coated with 1 light layer layer of New Skin, then removed after 7 hours.  Photograph taken 24 hours after paste removal.