Thanks, Jim:
Strange--in some 40 years of following the trail of the post-Civil War black regulars (ca l866-98) I have come across the term "buffalo soldiers' (in public print or private correspondence) less than 20 times- but I have tripped over the "N" word a lot-- both in the press and in letters/journals ("darkey" runs a close second, "colored" a distant third).
But then again--really not so strange given the times.
An aside--Pershing strikes me as the kind of fellow who could have put the K-bosh on his army nickname (and I'd bet he heard it more than once) long before the fourth estate cleaned it up.