In the West, there is a long-standing tradition of “cowboy coffee” making. Any time you are out in wilderness or elsewhere, caught without the comforts of home, you can make cowboy coffee by boiling water and coffee grounds together over a campfire. When you are ready to drink it, you can TRY to strain it with a pan’s lid or some other device, or you can just pour away. The trick is to let the grounds settle to the bottom your cup before drinking and whatever you do, don’t drink the dregs!
I’ve made cowboy coffee more than a few times in my life and apparently, it makes a pretty decent edible dye too! I had some wood ash (the “campfire” part) and tried dyeing with it alone. It was horrible, the pieces came out blotchy and weird.
So then, after talking to Michael Carroll, I resolved to use that ash successfully. I combined the ash with coffee grounds, mortar-and-pestled it into a paste, and voila! A pretty decent black emerged: