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 development controlling technique, without requiring complex mechanisms for blue color development that have been previously presented and techniques reproducing such mechanisms. Delphinidin-based anthocyanins, in which the both 3′； and 5′；-positions of the anthocyanin B-ring have been glycosylated, and flavone glycosides or flavonol glycosides as copigment are made to coexist in the cells of flower organ such as petals.
