Hmmm...that's a good question. NUPUR Henna is my lifeline..LOL!! Its the ONLY henna I use, and I've been using it close to 2years now
But I've never done an indigo treatment behind it, so I'd be interested in an answer too.
However, after monthly henna treatments for 2years, I do believe my hair has acutaully reached its henna "saturation". Its about as dark as its gonna get...I get no more color change anymore and I love it. My hair is now a
permanent auburn-ish/burgundy-ish/darkbrown/near-black....and only available under the sunlight...LOL!!