Final answer:
Acid-base indicators change color in response to changes in hydronium ion concentration, as illustrated by phenolphthalein's color shift from colorless to pink when moving from acidic to basic solutions. The statement is true.
Step-by-step explanation:
Acid-base indicators indeed change color in response to changes in hydronium ion concentration, making the correct answer to the student's question true. For example, phenolphthalein is a common acid-base indicator that is colorless in acidic solutions where the hydronium ion concentration is high (pH < 8.3) and turns pink in basic solutions where the hydronium ion concentration is low (pH > 8.3).
This color change occurs due to a shift in the equilibrium between the protonated form (colorless) and the deprotonated form (pink) of the indicator, following Le Chatelier's principle.