I particularly recommend this book as a visual source for historical re-enactors.
Too often there are descriptions of what dye-plants were used to color garments, but, no examples of what those colors would look like. This book provides clear, vivid color photos on a whole range of dye-plants grown during pre-medieval, medieval, Colonial, and later times. Additionally, it shows the same dye used on different fibers, sometimes with different mordants (fixers). Fiber samples include linen, wool, silk, and cotton.
I recommend this book to people interested in making clothing from "modern" material...it gives them the best opprotunity possible to try to find close color-matches. Alternately, it provides solid information to dye cloth by hand.
Also, the low price can't be beat!