Not the most exotic sounding dye material but don’t underestimate the onions or the onion skin. For me it has been a reliable, versatile dye that I can use on both protein and plant fiber. So far I’ve dyed wool, cotton, and soy silk.
Above, pre-alumed wool dyed with onion skins. The green is indigo over-dyed in the same batch. The plant:fiber ratio was .5:1 but I believe that I could have used considerably less dye stuff. The onion skins and fiber had been simmered for an hour and left to soak over night. The next day the dye still wasn’t exhausted so I over-dyed some previously indigo-dyed wool.
Copper and Iron after-baths darkened the color but ended up with similar shades. The Ammonia after-bath brightened a bit.
Onion skins are easy to save up and store. When I am shopping produce I sometimes tidy up around the onion bin.