In some flowers, a purple pigment is synthesized from a red precursor pigment. In the absence of all pigment, flowers are white. A pure-breeding plant with red flowers was crossed to a pure-breeding plant with white flowers. All of the F1 plants had white flowers. The F1 plants were crossed to each other, and the F2 consisted of 166 plants: 123 with white flowers, 32 with purple flowers, and 11 with red flowers. How do these results suggest that flower color is determined