The purpose of the present invention is to provide a breeding method for a plant having a blue flower color with a simpler blue color expression controlling technique, without requiring complex blue color expression mechanisms that have been previously presented and techniques reproducing such mechanisms. A delphinidin-type anthocyanin, in which the 3' and 5' positions of the anthocyanine B ring have been glycosylated, and a flavone glycoside or a flavonol glycoside as a copigment are made to coexist in the cells of a flower organ such as a petal of a plant.
