MOUSE PAINT!  This book by Ellen Stoll Walsh is a favorite.  Students learned about primary colors and how they are mixed to make secondary colors.  Two classes created their colors using primary colors on a palette to mix to secondary colors.  Two classes had paper with puddles of red, yellow and blue covered with saran wrap.  They finger painted without the mess by only touching the saran wrap.  they cut out the mixed colors and glued it to another paper to draw mice painting it.