This review describes the huge impact of phthalein dyes on multiple industries. Although phthalein dyes demonstrate several vital applications, there appears to be no review in the literature. Part 2 of the review focuses on developments in the chemistry and biological applications of phthalein dyes. The biological applications of phthalein dyes are grouped into agrochemical, biochemical, food, personal care, pharmaceutical and sensors applications. The importance of these dyes in various commercial products is also revealed, and patent analysis is provided in the Appendix. The uses of phthalein dyes in various fields are important but their growing popularity with fascinating colour change features is particularly notable. Part 1 of the review focused on developments in the chemistry and industrial applications of phthalein dyes. The industrial applications of phthalein dyes are grouped into building/construction applications, coatings applications, electronic/electrical applications and miscellaneous applications.