A substance that changes color to indicate changes in pH is called an indicator.

Here are some common examples of indicators:

* Litmus paper: Turns red in acidic solutions and blue in basic solutions.

* Phenolphthalein: Colorless in acidic solutions and pink in basic solutions.

* Methyl orange: Red in acidic solutions, yellow in basic solutions, and orange in neutral solutions.

* Bromothymol blue: Yellow in acidic solutions, blue in basic solutions, and green in neutral solutions.