In addition to my interest in Navajo weaving techniques, I'm also an active dyer, often with natural materials. One reference that I have found found to be extremely helpful is a book by Jenny Dean called Wild Colour. It was published in 1999, and is now out of print. When it can found on the used book market, it sells for about $100. Jenny has tried to persude the publisher to reprint the book, but they don't believe that there is ia large enough market for it. Jenny doesn't own the copyright to the book, so self-publishing options like lulu.com aren't possible.
I've started a page on Facebook advocating a reprint, and you can become a fan of the page if you agree with me. The link for the Facebook page is http://www.facebook.com/pages/Wild-Colour-The-Complete-Guide-to-Making-and-Using-Natural-Dyes/117794646494. You can see a limited preview of the also out of print U.S. edition on Google books. You can also find Jenny's current dye wisdom at therWild Colour blog. If you don't happen to have a Facebook account, but would still like to support the reprinting of the book you can writie to the publisher directly at email@example.com.
I hope that you're not offended by this somewhat off topic post! I promise to start a Natural Dyes group on Weavolution immediately.
Nizhonigo nanina doo (may you walk in beauty)