@Suave Thanks for the compliment. Occasionally I get it right, like a broken clock, but not quite as often.
I did a little digging, mostly online, before tying that pattern and came across a few variations, including Bates' version. I assume bucktail, as Bates uses the word, refers to the style of the fly.
The fly seems to have a bit of a storied history, even from it's creator Frank Dufresne, who apparently told a few different versions of how it was named. Most versions agree that is was based on a lure Dufresne saw being used by the Eskimos on the Kobuk River in Alaska back in the 20's. Given the era and location, I'm not sure what options he would have had for materials. My opinion with these older patterns is the creators may have had a preferred material, but they would use whatever they had on hand and didn't fret too much about it.
Anyhow, while searching online I came across a variation posted on the Global Fly Fisher site that had a dubbed body of white rabbit. I thought it looked pretty cool that way, and as I was recently gifted a small patch of pre-CITES polar bear from a very generous acquaintance, I thought hey, why not use the underfur as dubbing. So yeah, that is polar bear for the body and wing. (And you're right, the underfur, chopped into shorter pieces, looks and dubs similarly to seal.) And it has that nice cream or off-white color to it. The guard hairs are a bit yellowed, as you noted. Not sure if that is a natural variation of the hair or due to its age. In any case, the polar bear hair does have a nice translucence that doesn't really come through in the photo.