The degree and type of pigmentation are influenced by both the relative ratio of eumelanin (brown-black pigment) to pheomelanin (yellow-red pigment) and the number and distribution of melanosomes.

Pheomelanin is responsible for the pinkish hue of specific anatomical areas such as the lips, nipples, vagina, and glans penis. https://www.ncbi.nlm.nih.gov/books/NBK459156/