Supplies: Whole milk, food coloring, dish soap (dawn works best), food coloring, and a shallow bowl or plate with ridges to contain liquid (At school, we used petri dishes.)
Pour milk in bowl and put a drop or two of food coloring in the milk. If you only use primary colors, you could relate this activity to mixing colors.
This happened when we put the color in the too warm milk. cool
Add a drop of dish soap in the middle and watch the colors swirl. The colors will disappear, swirl into each other, and mix. Eventually, the colors swirl together so much that it turns gray.