I have found that the book Mouse Paint is a fun way to show children what happens to primary colors when they become mixed. I have the colored mice which go with the story, but I use peanut butter jars. I have all the peanut butter jars covered with construction paper. For example, the red mouse is in the jar covered with the red construction paper and so on. After we have read the story and the children think I have performed magic we then use a long piece of white paper to reenact dip one side of the stem in undiluted red food coloring and the other side of the stem in yellow food coloring, after a few days you will see that the carnation will begin to turn orange. Repeat the process using yellow and blue food coloring and red and blue food coloring.