I don't think that this is a leucistic bird: only the tail feathers are
affected, all but one tail feather is white and one remains normal
color. Here's a link to an article which I found in pursuing my
curiosity about the bird:
https://academic.oup.com/beheco/article/17/6/1046/319763

My best guess now is that this was a a "fright molt" instance. We do
have a neighbors cat, and have put up a wire barrier around the bird
mound and feeders. Nonetheless, the little feline still tries very hard
hoping we are not watching. I also found a couple of blogs mentioning
that Black Capped Chickadees can replace the feathers with white ones
after a fright molt nd that subsequent molting will replace those with
normal. Anyone wanting to see the white tailed Black-Capped can send me
a private email here. I also will be putting the photo on my website
later today [Sept 30]