Sorry for late response Korkscrew. Henna makes my gray strands a vibrant red but my naturally dark hair is just shinier. Amla darkens my hair but really doesn't change my gray. I have used a mix with equal parts henna/Amla & my gray strands were a bronzey red color. HTH.
So, I used my amla + coconut oil and I can't really report much difference from using plain coconut oil to pre-poo. :S Sorry I don't have anything more interesting to share!
Sat in my henna gloss yesterday for about an hour then did a moisturizing deep conditioner with Jessicurl. My hair is stronger and happier. It also has a lot of sheen and was particularly manageable. I will use the conditioner each week so I can give a full review of the effects. So far so good, my hair did seem 'plump' this morning. There has been no change in color.