Potions are all chemicals, and it depends on what their ingredients are to make them appear. Are based on chemical principles.

If iodine is used as starch solution, the word is blue;

If litmus is used in acidic solution, litmus turns red in acid and blue in alkali;

If it is an alkaline solution, litmus and phenolphthalein can be used, but it is best to use phenolphthalein, which is colorless and turns red when it meets alkali.