In flower color a P is required for it to exhibit purple color. This can only happen if a dominant allele is present for another characteristic. The C characteristic has an effect on the color of the flower. Polygenic Traits . Quantitative traits or having 3 sets of alleles for a characteristic.
Skin color is polygenic.
There are 6 genes responsible for this characteristic. All the other genotypes are intermediates of these combinations. Click here for related links.