I call this accidental art. It's suitable for any age from about fourth grade through adult. Students take any color water color except brown and black. They cover their paper with shapes of color, with no colors overlapping or touching. They repeat colors and shapes as they wish. They wash their brushes between colors so each color remains true. Then they let their creations dry for one day. On the second day they use a black fine tip marker and decide a different texture to put in each color -- little crosses, circles, lines, etc. Filling the colors with these textures creates an attractive piece of art and teaches them about unity and variety and pattern and texture.