We use water color pens on white paper. We use Mr. Sketch pens. The Ontario Science Center also has an online activity which allows shockwave equipped computers to explore additive and subtractive color mixing. Rods have rhodopsin which light breaks into retinene and opsin releasing an electron and energy. Resulting in a nerve impulse.
Cones act similarly but have different tunings.
Most people have 3 cones Red Green and Blue named after their peak response. Cones are named after the color of their peak sensitivity not after the color you see when they fire alone. However red light and green light also fire both cones equally resulting in a perception of yellow. Many different combinations of light can result in the perception of the same color. Even so, you can perceive over a million different colors.