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 ( Centaurea cyanus), [1] and the identical pigment was isolated from a red rose in 1915. [2] The difference in colour had been explained as a difference in flower-petal pH, [2] but the pigment in the blue cornflower has been shown to be a supermolecular pigment consisting of anthocyanin, flavone, one ferric ion, one magnesium and two calcium ions [3] forming a copigmentation complex.
The molecular formula of protocyanin complex is of the type of C366H384O228FeMg.