So I'm going to henna for color. I mixed henna w/ lemon juice, coffee, and water. It's been sitting for about 12 hours now. My hair is black and I want it blacker if possible w/ the added shine. I don't have indigo to add at this time. My question is this: Do you think it will make any difference color wise if I let it sit longer or have I let it sit long enough to get as dark as it can w/o indigo? Thanks, Ladies!