Why might traits such as skin color be fairly consistent within a racial group, but alleles for skin color aren't consistent?

A) There's no relationship between alleles and skin color.
B) Skin color is influenced by many genes, so several different gene pools can produce the same skin color.
C) Only one gene is important in skin color, and when analysis is limited to that gene, there's clear evidence of a long separation of groups.
D) Few allele variations between groups are just what you would expect if races were genealogical species.