I was shown this book at our weekly rug hooking group meeting. It's called Hand Dyeing Yarn and Fleece by Gail Callahan. Here is some information from the back cover:
Take control of your colors! Apply your dream shade to natural-colored yarns and fleece. Transform outdated yarns with fresh new colors. Create self-striping and multicolored yarns. It's all possible with Gail Callahan's simple recipes, designed to work in your own kitchen. So, fire up the oven or your slow cooker, clean out an unused microwave, or grab a sturdy kettle—you'll love the results of playing with heat, color, and fiber.
I looked through this book and found the methods to be clearly explained, with wonderful photos to accompany the text. Many of these techniques will be familiar to rug hookers who dye their own wool. What I liked about it was that you are encouraged to overdye small skeins of yarn left over from other projects by "marrying" them with a single dye formula. Here is a link to the spiral bound edition on Amazon.com.