Chromatography
Chromatography is a way to separate the hidden colors inside a mixture by letting a liquid carry them apart on paper.
Drop a black marker dot near the bottom edge of a paper towel. Then dip just the very bottom of the towel into a shallow bowl of water. The water travels up the towel and carries the ink with it, but some colors in the ink are lighter and move farther up while heavier colors stop lower down. After a few minutes, the single black dot has spread into a column of separate color bands.
Explaining chromatography by grade level
Draw a dot with a marker on a coffee filter, then dip the edge in water. Watch the water creep up the paper. As it moves, the dot splits into different colors. One marker had many colors hiding inside it. The water pulls them apart because some colors travel faster than others.