It is not easy to color grey hair with brown shades using natural hair dye - henna and indigo. It's doable, certainly, but time consuming. If using plant-based hair color is of the ultimate importance, regardless of time, then by all means check out the following videos. These videos demonstrate how to touch up grey by using a mixture of henna and indigo to achieve a dark brown color. Only Parts 1 and 2 are completed (this is a long process, remember?) and they include co-washing and Part 1 and mixing henna in Part 2. These are my first videos and I have a lot of room for improvement but I hope they are understable.
The following video is how I mix my henna which I did BEFORE I co-washed my hair....