Color mixing on a tray

Fill three small cups with water. Add a few drops of food coloring to each (one red, one yellow, one blue). Put on a tray. Add a dropper or spoon and an empty fourth cup.

Pick up the dropper. Take some red. Squirt it into the empty cup. Take some yellow. Add it to the same cup. Watch it turn orange. "Oh."

Wide-eyed wonder. Methodical mixing. The discovery that all three together make brown. Then the question "what happens if I do all the red?"

Use ice-cube trays for many small mixes. Add a paper coffee filter to soak up the color into a tie-dye look. Switch droppers for turkey basters for harder volume control.