Before wool is made into yarn it is usually washed (sheep can get pretty mucky!) and sometimes it is dyed. It's easy to dye wool in a rainbow of colors, basically all you need is pigment and acid. The acid is necessary for the wool fibers to absorb the pigment so that it will be color-fast after the dying process. Heat is usually used to speed up the color absorption.
All of the wool in the picture ^^above^^ was colored with non-toxic dyes, either food coloring or Kool-Aid. Yup, Kool-Aid! One small package of Kool-Aid comes complete with enough pigment (food coloring) and acid (citric acid, ascorbic acid) to dye one ounce of wool. If I use plain liquid food coloring then I would add vinegar for the acid. I have fun mixing different flavors of Kool-Aid and/or drops of food coloring to get just the right colors!
