at one of the natural wool classes at my favorite wool store in kyoto, kin no hitsuji, we dyed wool with gobaishi, ごばいし 五倍子 a japanese gall that is created on japanese sumac (i think...it was a little complicated and hard to understand in japanese!!). with just alum and gobaishi, it didn't really change the color too much, but with iron, it turned a lovely heathery purple.
the gobaishi galls boiled for an hour in a mesh bag, they turned mushy
into the pot with iron added
if anybody out there knows more about gobaishi, i'd love to hear from you!