Absorption, Dissolving, Concentration, Water stratification, and color mixing are the key science concepts that plays major role in rainbow skittles science activity. When you pour the water in the middle of the plate, water makes the skittles wet. As soon as the skittles dissolved in water, they start releasing their own colors in a streak because of water stratification. Water stratification is nothing but non-mixing up of colors as the colors show different chemical properties.