Dyeing with red onion skins blows my mind every time. How do these red skins turn in to yellow/green colours1? I have dyed wool yarn before with red onion skins and got an amazing strong colour. This time the colour was a bit lighter, but I think that really depends on the material. The lace I dyed turned out much stronger and this old sheet fabric that I have always gives lighter colours.
I mordanted my fabrics before hand with taro root powder and alum. You can read about it here. The dyeing process doesn’t differ from dyeing wool yarn or from dyeing with normal onion skins. I have written a good blog post about that here.