Hein van Grouw comments as follows: The plumage colour is obviously the result of a pigment aberration. Brown and Dilution are the most likely candidates. In fresh plumage it is quite easy to tell them apart but in old and worn plumage (like in this bird) it is more difficult without seeing the bird 'in the flesh'. However, the fact that this bird is a male (according to the red head) rules out the mutation Brown. As Brown is recessive and sex-linked, 99.99 % or more of the birds with this mutation found in the wild are females.

So the mutation causing this woodpecker's aberrant colouration is a form of Dilution. Dilution only affects the melanins and original black feathers will turn grey. Carotenoids (yellow and red) are unaffected and often seem to be even brighter in colour as the overlaying melanin is reduced. Diluted melanin is very light sensitive so feathers can bleach even further in the (sun)light and the grey feathers then will bleach into 'dirty white'.