I already have some books with swatches in my dyeing supplies: Triple Over Dye 1 and 2; The ATHA Dye Book of 2011; and Seasons of Wool by Angela Anderson of Pioneer Primitives, but I need to begin to expand my library.
Lately, I've been buying Pro Chem dye colors vs Cushing. Pro Chem comes in a screw top jar instead of a tiny plastic envelope, and the amount of dye is greater. The Cushing colors are softer. Pro Chem color is more vivid. I finally purchased the Pro Chem color cards made with yarn.
I purchased the book Primary Fusion by Ingrid Hieronimus and it's accompanying wool swatch set from Ragg Tyme Studio.
The Primary Fusion system dyes 58 colors from 4 Pro Chem dyes, Magenta 338, Blue 490, Yellow 119, and Black. The book introduces basic color theory and should be very easy for the beginning dyer to use. Ingrid states on her first page: "For those of you who are already dyeing, this system is so comprehensive that you will learn how to vary a formula to produce the exact colour you want." This is what I'm after....