Protocyanin

Protocyanin is an anthocyanin pigment that is responsible for the red colouration of roses, but in cornflowers is blue. The pigment was first isolated in 1913 from the blue cornflower, and the identical pigment was isolated from a red rose in 1915. The difference in colour difference was previously explained as a difference in flower-petal pH, but the pigment in the blue cornflower has been shown to be a supermolecular pigment consisting of a complex of anthocyanin, flavone, one ferric iron, one magnesium and two calcium ions.