Thymolphthalein is an acid-base indicator. Its chemical formula is C28H30O4. Thymolphthalein has two color stages in an aqueous solution.
Figure: The color of thymolphthalein in solution at various pH levels. At pH 0 - 9.3 the solution is colorless. At a pH of 9.3 - 10.5 it changes from light blue to blue.