Acid vs. Base: The Color-Changing Experiment!

How does chemistry turn this liquid from clear to deep magenta? The liquid in the beaker is phenolphthalein, a chemical indicator that changes colors when exposed to a high pH. In this experiment, the phenolphthalein is combined with a small drop of ammonia, a strong base, causing it to change color. It then changes back to clear when it is combined with a drop of vinegar, an acid with a low pH, which balances the pH and neutralizes the base!