To introduce downy mildew resistance from a yellow-colored resistant cultivar, 'Santero', into a yellow breeding line, OT803, the F1 hybrid was produced by crossing Santero and OT803. The bulb color of the F1 hybrids became light pink, suggesting involvement of complementation between the DFR-A and ANS genes in the onion anthocyanin biosynthesis pathway. Since Santero contained active DFR-A and inactive ANS alleles, OT803 was assumed to harbor active ANS and inactive DFR-A alleles. However, some yellow-colored individuals of OT803 were shown to contain the homozygous genotype of the active DFR-A