Provide students with a pipette, wax paper, paper towel and 3 small cups - one with blue water, one with red water and one with yellow water. Food coloring can be used to color the water (a small amount will go a long way), but food coloring does have the potential to stain, should the water spill. Another option is to use the True Color Tablets available from Steve Spangler Science, which do not stain.
Students use the pipette to place drops of colored water on the wax paper. They can then drag the different colored drops together and watch the colors mix.
Challenge your students to make the entire color wheel. Or see how many different shades of green they can create by mixing varying amounts of blue and yellow water. Most importantly, allow them time to explore on their own to see what they can learn.