I used to use: henna plus ReaLemon
Then I switched to: henna plus tapwater
That’s it. The only thing is that if your tapwater is very alkaline, that could prevent the henna from reaching sufficient acidity on its own. There are a few ways around this: Use the water with only a small amount of the acid, make the water into chamomile tea first using any cheapo chamomile teabags (will acidify the water a bit, and also is supposed to help with rinsing slip but I haven’t tried), or, buy distilled water at the store to use.
I have recently come to believe about the Yemen that it does release dye faster than other origins or crops, and I suspect it may have a longer continuum of dying time also. I have got the reddest and darkest results from it by mixing it with only water, applying pretty much right away, and leaving on a really long time.
I really think you don’t need 900 ingredients. But the one additive I would possibly advise is the bit of salt with the indigo. It is supposed to help with colorfastness. The one time I did add indigo, I failed to remember about the salt, and the indigo did wash out in days, lol.
If you start with a very simple mix, and then you really don’t like the henna smell or something, you can then experiment with adding the ginger or cloves or whatnot. I don’t believe they do anything noticeable or lasting to the color, it’s just a smell thing. Henna is strong dye, I don’t see anyone really dying their hair permanently with only coffee or cloves."