Considering the fact that there were literally hundreds of Native American tribes with dozens of legends and traditions each I am sure that some had a taboo on killing white buffalo and other white animals. However, I doubt that there was wholesale protection unilaterally awarded to any creature. I have tried to research it and my search winds down rabbit hole after rabbit hole. It appears that most of the perceived protective spirituality associated with white or albino animals is a relatively new idea. Earlier concepts appear to have been more of a covetous nature, as in shoot, skin, possess, and thereby receive the medicine/power.
Teddy Roosevelt is said to have offered $5,000 for the skin of a white buffalo that had a treaty signed on the back of it. The buffalo was killed by the Cheyenne in 1833.
Sacred does NOT mean protected. There are multiple Native American legends associated with white deer that refer to the animals as sacred and then go on to indicate that they were hunted. A Chickasaw legend that I read recently refers to a young warrior that never returned from a quest to kill a white deer for his bride-to-be. In turn the woman never married. According to the legend the white deer was thereafter "sacred" and a wedding dress made of white deer hide the ultimate symbol of eternal love.
For me personally, as a hunter, I struggle with the notion of attaching any protective aura to wild game animals based simply on appearance. To me, all game animals are beautiful. It seems a contradiction to single one out for protection based on some near anthropomorphic idealism. After all, isn't that what anti-hunters do with all game?
What I think happens more often than not is that a white deer shows up in somebody's back 40 and because it is more easily identifiable than the rest of the herd it earns a name and becomes something of a "pet". After that it becomes something that they scan the treeline looking for every time they cross from the barn to the house. After a few encounters they have some sense of connection to it and naturally become reluctant to kill it. I can buy that and would probably feel the same way.
My dad used to hunt a stand that he would see countless does and fawns from on a daily basis. He had them all named. When it came time for doe-days he was worthless as a manager. If there had been a white one in the lot we might have had a fist fight!
Very cool pictures, by the way!