1, pH change: The change of pH value leads to the change of thymolphthalein color. If the pH value of the solution changes, from acidic to alkaline or neutral, and vice versa, the color will change.

2, intake of air: contact with air can also cause color changes. Thyme phenolphthalein is a sensitive chemical, which may change color due to oxidation when exposed to air.

3. Reaction products: The existence or reaction of other chemicals leads to color change. There are other chemicals in the prepared indicator solution, which react with thymophenolphthalein to produce color change.