I did some dying with onion skins. The colours turned out really well, I think. I used the same dyebath twice and maybe I'll use it another time, if it doesn't start to smell funny (it's five days old ).
I mordanted the first batch with 15% alum and the second with alum and a pinch of cream of tartar. The greenish colour is Gotland wool, the rest is Friesian milksheep. So far I dyed 600 grams of wool with 300 grams of onion skins.