Senna is another natural alternative to chemical color.  Henna is typically used by people with darker hair and senna is used by people typically with light or blonde hair.  The indigo will give you raven black hair if used immediately after a henna treatment or if you mix the two together you'll get dark brown hair.  Cassia has no color at all on the hair.  Gave more info than needed?? Just FYI   P.S.  always do a harvest test so you won't be surprised or shocked with the end result.