Even in the days of Saml. Clemens, it was Huck, Pap, and the river crowd that used the "N-word", not Aunt Polly, Judge Thatcher, or any of the well to do townsfolk. Even in those days it was considered low, Clemens used it in Huckleberry Finn to make a point -- it was the only way human debris like Pap could find to hold themselves above SOMEbody.
"Negro" is actually the correct anthropological term and was not considered derogatory until the "Black Power" movement of the sixties. My grandmother not only used that term, she also used "Negress". Now THAT would get Al Sharpton's BVDs in a bunch. Some older ladies of color in my youth preferred the term "colored" and of course their preference was honored.
Nobody said "darky" outside of a minstrel show, certainly not a lady.