One of my favorite books on color mixing is "Mouse Paint" by Ellen Stoll Walsh. In this book 3 mice dip themselves into three different paint jars: red, blue and yellow. They quickly learn that when they mix the colors they create whole new combinations. Children learn that if you mix red and blue together you will get purple, if you mix yellow and blue you make green, and if you mix red and yellow you will make orange.
Take a trip to the Burlington Public Library and take out a copy of "Mouse Paint." When you finish reading this story with your child be creative and play with colors. This can be done several ways. If you are up for mess you can certainly do it with paints. You can also recreate this activity by using water and food coloring. Put water in 3 cups and add a few drop of food coloring to the water. In cup one add red food coloring, in cup two add yellow food coloring and in cup three add blue food coloring. Using an eye dropper have the children mix the colors between cups and let them explore what happens when you mix the colors together. You might want to guide them at first and refer back to the book to see if they can recreate some of the colors. If left on their own they will most likely mix all of the colors together at once and make black.
Another great book on color mixing is "Little Blue and Little Yellow" by Leo Leoni.
This book also focuses on color mixing and can also be used to teach colors and what happens when you mix colors together.