How do we explain the white feathers of an albino peacock?
The surface structuresa that are responsible for the structural coloration of peacock feathers are actually barbules and rods made of the very same biopolymer that is responsible for pigmentation in many other animal species, namely melanin. Just as in other animals, melanin is produced in the melanocyte cells which reside in the skin's epidermis. The conditions of albinism or leucism are due to mutations to genes responsible for melanin expression in those cells, or their absence. So although structural coloration is resposible for the colorful peacock feather, it is the same mechanism that leads to colorless feathers as in other animals.

Reference

a Zi, Jian, et al. "Coloration strategies in peacock feathers." Proceedings of the National Academy of Sciences 100.22 (2003): 12576-12578. https://dx.doi.org/10.1073/pnas.2133313100