There is provided a gene coding for the amino acid sequence listed as SEQ ID NO: 2 or SEQ ID NO: 70, for example. Co-expression of the 4'CGT gene and AS gene in a plant lacking natural aurone synthesis ability is carried out to successfully accumulate aurones and alter the flower color to have a yellow tint. In addition to the expression of both genes, the flavonoid pigment synthesis pathway of the host plant itself is inhibited to obtain flowers with a more defined yellow color.