The colour of the feet is due to presence of melanin. Some varieties are produced by a change in melanin production ie Cinnamon, Ino, Lacewing. Some although change melanin in the body do not in the feet unless combined with one of those previously mentioned ie Cinnamon Dilute. Pieds lose the melanin in the feet due to total absence of melanin due to the action of the "pied gene" which is a difference action to the one that produces Cinnamon etc.
Young birds can sometimes show pinkish feet as they have not yet moulted and gained the full compliment of melanin in the skin cells.