Wikipedia
Metalloanthocyanin
A metalloanthocyanin is a chemical complex giving color to petals of certain plants.
These complexes are self-assembled, supramolecular metal complex pigment composed of stoichiometric amounts of anthocyanins, flavones, and metal ions. The various colors, such as red, mauve, purple, violet and blue, in Hydrangea macrophylla are developed from one simple anthocyanin, delphinidin 3-glucoside foming complexes with metal ions.