Phenolphthalein is a common acid/base color indicator. In it's protonated form, it is colorless, and in its un-protonated form it is pink. Which of the following statements is true of phenolphthalein? Choose all that apply. The color of phenophthalein cannot be predicted by pH. Phenolphthalein is pink at high pH. U Phenolphthalein is colorless at low pH. Phenolphthalein is colorless at high pH. U Phenolphthalein is pink at low pH.