Colour meanings are not fixed — pink and blue's modern Western gender associations only solidified in the mid-20th century, purple's royal association outlived the economic scarcity that originally created it, and green's environmental-movement meaning is barely a century old.
Pink and blue were not consistently gendered in the early 20th-century United States, with some contemporary sources even suggesting pink for boys and blue for girls, well before the now-familiar convention solidified by the mid-20th century.
Changing meaning · United States · early to mid-20th century
Historical gendering conventions varied and were not universally agreed even within the same period and country.
Purple's association with royalty persisted in European heraldry and court dress long after Tyrian purple dye production had declined and synthetic purple dyes had made the colour widely affordable — a symbolic meaning that outlived its original economic cause.
Changing meaning · Europe
Green became the internationally recognised colour of the environmental movement over the course of the 20th century, a meaning layered on top of, not replacing, its much older associations with nature and growth.
Changing meaning · global · 20th century onward
Historical claims above are scoped to a specific period, region or culture where relevant — none are presented as a single universal fact. See methodology.