Hair is a textile, and henna is a natural hair color. What is interesting is that you can shift the color by combining it with indigo. Click images for larger versions.
I finally mixed up the henna and indigo I bought to color my hair. It's a good overall conditioning treatment also. My goal was to not change the color much, so I used 3 parts henna and 2 parts indigo to keep it from getting too red. The henna is mixed with a weak acid (I used orange juice) and sits overnight to extract the dye. The indigo is then mixed with water and then combined with the henna and more water until it's a semi-solid glop.
The henna is from Pakistan, which was recommended for brown hair. It's what is sometimes called "bridal quality henna," a fine powder also used for traditional hand and foot designs. I'm not really clear what "partially fermented indigo" means here, but the powder has the yellow-green color of a partially reduced indigo vat. (If you really want to know what that means, go look here.) Supposedly it "isn't a textile dye" (but hair is a textile!) I haven't tried it but given the quantity required I'll likely stick to the normal stuff for other fibers.
This horrible picture is what my hair looked like before.
This is what it looked like for three hours while I sat around with a large quantity of glop on my head. It only dripped a little. I am very happy we have some black bath towels.
The recommended amount to use is 500g dry for long hair. I had to mix it in one of my dyepots because I didn't have a metal or glass bowl large enough. This seemed like an absurd amount until I tried to actually get all of my hair covered, down to the scalp. Which is rather annoying to do alone. I had to clean the walls and floor when I was done. I should look for an Indian hair salon next time, at least for the application.
After washing mud out of my hair for half an hour, it looked like this, a little darker with a hint of red.
So after all that my hair was more-or-less all the same color, but the ends were in bad shape. So I got the bottom hacked off. Oh, and I made that jacket too. It's for somebody else but he wasn't around so I got to wear it.