pie bald is a genetic condition, mostly its a sign that deer are overpopulated, now I'm playing on memory here so the numbers may not be exact.
1 in 267,000 whitetails carry the gene that makes it possible for the offspring to be missing patches of skin pigment, they may be normal but both parents must carry the gene for it to be possible.
albinoism (lack of pigment anywhere, thats why the eyes appear red) occurs at the rate of 1 in 1 million. its very rare.
back to the piebalds, 1/267,000, so lets do the math, there are 2 deer in 534,000 carrying this gene who happened to hook up, it would take an extremely high population for that to happen, here in wv, the conservation people will encourage you to harvest them.
A couple I've taken in the past

RR