The correct answer is D. Defective migration of melanoblasts.

Piebaldism is an autosomal dominant condition characterized by stable, benign leukodermic patches. These patches contain pigmented and hyperpigmented macules within them and a white forelock with underlying depigmented skin. Most causes of piebaldism are due to mutation in the c-kit gene, which is essential for the normal development and migration of melanocytes from the neural crest. A similar forelock can also be seen in Wardenburg syndrome, an autosomal disorder of the neural crest development due to mutation in PAX3, MITF, and SOX10 genes. Four clinical subtypes have been described, but other clinical features such as deafness, heterochromia iris, and dystopia canthorum are also present.

Vitiligo is due to the absence of functional melanocytes due to autoimmune destruction, although the pathogenesis of vitiligo is multifactorial. A defect in melanin synthesis causes oculocutaneous albinism. Overgrowth of the hyphal form of Malassezia furfur causes pityriasis Versicolor. Exposure to phenols/catechols and other substances may produce chemical leukoderma.

References:

Bolognia, J., In Schaffer, J. V., & In Cerroni, L. Dermatology. Elsevier,2018. Ch.65