Speciation in angiosperms can be accompanied by changes in floral colour that may influence pollinator preference and reproductive isolation. McCarthy et al. investigate whether floral colour shifts accompany allopolyploidy (interspecific hybridization and genome multiplication) in the genus Nicotiana (Solanaceae), and find that floral colour categories have arisen multiple times independently. Comparisons with their progenitor diploids show that some polyploids have unexpected floral colours when perceived by at least one pollinator type. Nicotiana tabacum has a transgressive floral colour due to the inheritance of anthocyanin from its paternal progenitor and a plastid phenotype like its maternal progenitor. They conclude that floral colour evolution in Nicotiana is weakly constrained by phylogeny, but colour shifts do occur in association with both polyploid and homoploid hybrid divergence.