Final answer:
A change in the color of an indicator is evidence of a change in the acidity of the solution. Indicators change color over a specific pH range due to the change in concentration of different forms of the indicator molecule. For example, phenolphthalein is colorless in acidic solutions and pink in basic solutions.
Step-by-step explanation:
When an indicator changes color, it is a clear evidence that a change in the acidity of the solution has taken place. Indicators are substances that undergo a pH titration and change color over a specific pH range. The color change is a result of the change in the concentration of different forms of the indicator molecule. For example, phenolphthalein is colorless in acidic solutions and pink in basic solutions.