Answer the following question given this paragraph: 

An acid-base indicator is a substance that displays different colors when in the presence of an acid or a base. How does that work? An indicator is a weak acid that ionizes within a known pH range, usually about 2 pH units. We can represent the protonated form of the indicator molecule as HIn and the deprotonated form as In − . The following equilibrium exists for the indicator.


Q: A substance that displays different colors when in the presence of an acid or a base is called what?


A:
an acid-base indicator