There are a couple of comms on Ravelry for natural dyeing that are fascinating. I am a bit warey of nasty mordanted ones. I don't have the room to keep separate pots etc.

https://waysofthewhorl.wordpress.com/2011/04/06/natural-dyeing-take-2-onion-skins/ has a range of colours they got.
Pretty sure on the dye comm they talked about green from the red onion skins but a lot of my google results were reddy/brown and green when iron was added as a mordant I think. Or Alum
I don't remember.

I dyed with tea. Used it for Watson's skin tone. So british! Actually I think I used it for the porny Weasley thing I did too.

I boiled the shit out of the tea and then added the wool and let it boil in the pan. I was dyeing it for felting not spinning though. It is very slightly felted so not so great for spinning.