Review on Swiss Mist Brown Henna Natural by Becky Chopra

My hair is dark brown. Although I have a lot of gray hair. Got it to cover these. When I mixed this with warm water, the mixture was green. I hesitated but used it anyway. I only got out after 20 minutes because of the green. I was very happy with the dark brown part, but I keep seeing more and more green strands. It's been at least a few weeks since I've used it. I have ordered more but am considering switching to another natural brand. Did I just do it wrong? I really want to find out. Everyone?