What colour is phenolphthalein in a solution of pH below 8.3?

1. Phenolphthalein is colourless while the hydronium concentration stays above 5.0 x 10^-9 M. 2. That concentration corresponds to a pH of 8.3. 3. So below pH 8.3 the solution shows no colour from the indicator. 4. In more basic solutions, above pH 8.3, it turns red or pink. 5. The colourless to pink change is sharp, which makes it easy to read. _Source: OpenStax Chemistry (CC BY 4.0), Ch 14 "Acid-Base Equilibria", section 14.7 Acid-Base Titrations_