…and of the entire body, actually.
One of the more unusual sights I saw on my morning walk today. There is no blending into your environment when you are this white and stand out against deep green vegetation and dark brown bark. I can’t imagine that white squirrels have a long life expectancy, but maybe this one will survive until it snows, and get the last laugh after all.
White-furred gray squirrels may be true albinos that cannot manufacture melanin pigment in either their skin or eyes, or their skin pigment expression may be turned off, while they retain their dark eye color (Leucism or Leukistic).
True white squirrels (non-albino) are more common than you might think — for a recessive trait that seems to be an advertisement to predators. In the areas where they occur (see map below), the white variant makes up about 25-30% of the population, exactly what the Mendelian genetics of a recessive trait would predict. This is discussed in far greater detail here. In comparison, the incidence of true albinism is far rarer (e.g., only 0.006% of humans exhibit the albino trait).
It turns out there are a number of organizations and communities that celebrate their white squirrel populations with festivals, webpages, fieldtrips, institutes for the study of white squirrels, etc. Who knew white squirrels were so popular!