Bennie:
Your guess is as good as mine re when black soldiers first accepted the term buffalo soldiers--and if they saw the term as a name given in respect. So far I know of no documents to pin down a date--none.

But on the origin of the name business-a lot of current published
stuff can be traced back to what William Leckie wrote in his l967 pioneering study of the black cavalry regiments--The Buffalo Soldiers: A Narrative of the Negro Cavalry in the West.

Here's what Leckie wrote in his text:
"It was about this time [a reference to very late l860s or early 70s] thaty the Indians gave Negro troopers a sobriquet. Called all manner of names--"Moacs," "Brunettes," "Nigger," "Africans"--by all manner of people, they were dubbed "buffalo soldiers" by their red antagonists. Men of the Tenth, and later of the Ninth, accepted the term and wore it proudly. Indeed, the most prominent feature of the regimental crest of the Tenth Cavalry was the buffalo [see my earlier post on the l0th Cav general order from Ft Eathan Allen]

Well--to put a very fine point on the above: Leckie does not say by what date soldiers of the 9th and l0th accepted the term. As for wearing it "proudly"--probably,maybe, no way to know for sure.

It is important to note that Leckie's footnote support for what he wrote above does not refer to any period or even secondary sources.
His note is his opinion as a professional historian. Here's what he wrote in this note:

"The origin of the term "buffalo soldier" is uncertain, although the common explanation is that the Indian saw a similarity between the hair of the negro soldier and that of the buffalo [I'll bet Leckie had read Mrs.Roe]. The buffalo was a sacred animal to the Indian, and it is unlikely that he would so name an enemy if respect were lacking. It is a fair guess that the Negro trooper understood this and thus his willingness to accept the title."

A "fair guess"--you bet. A reasonable conclusion--maybe. Something based on verified period documents--not even close.
But Leckie did play fair--he put his thoughts in a note--not in the body of the text--and he used the
qualifier of "a fair guess."
Other writers--lots of them--have not been so carfeul--and you know as well as I that over the past thirty years or so Leckie's guess has become enshrined as fact and an underpinning of the tale of the Buffalo Soldiers.

Exit comment: I have loaned out my copy of the Leckies' 2003 revision (William Leckie was joined by his wife in this revision) of this book and I do not recall if he has modified his original views on the name origin.

PS On Leckie's claim that Indians would not use the name of an animal they considerd sacred unless it was bestowed in respect. Years back a scholar friend of mine put together a list of genuine Plains Indian person and place names where the word buffalo was probably not used in a tone of respect: names such as Dumb Buffalo, Slow Buffalo, etc.