Provided is a method for producing lilies containing a blue pigment (delphinidin) in the petals thereof by introducing a foreign gene into lilies. The method pertaining to the present invention is a method for producing lilies containing delphinidin in the petals thereof, including the following steps: introducing, into a lily, a F3'5'H gene derived from a campanula and comprising a nucleotide sequence encoding a peptide having flavonoid 3'5'-hydroxylase (F3'5'H) activity, such as a nucleotide sequence represented by SEQ ID NO: 1 or SEQ ID NO: 11; while also introducing a F3'H gene fragment derived from a lily and comprising a nucleotide sequence encoding a peptide having flavonoid 3'-hydroxylase activity, such as a nucleotide sequence represented by SEQ ID NO: 3 or SEQ ID NO: 16; and inhibiting the expression of endogenous F3'H expression, which acts on cyanidin synthesis in lily petals, while the F3'5'H gene that has been introduced acts to cause the synthesis of delphinidin.