Bromocresol purple or 5′,5″-dibromo-o-cresolsulfophthalein, is a dye of the triphenylmethane family and a pH indicator. It is colored yellow below pH 5.2, and violet above pH 6.8. In its cyclic sulfonate ester form, it has a pKₐ value of 6.3, and is usually prepared as a 0.04% aqueous solution.