When I was growing up in Texas in the 1950s it was always an adventure to listen to a politician trying to refer to black people in the presence of Yankees.
For some reason, no politician south of the Mason-Dixon line seemed able to pronounce knee-grow. The word always came out as nih-gro, nig-rah, nih-grah and sometimes knee-grah.
Basically, “Nigrah” was simply the N-word for polite society. It may have been different in other locations, but where I grew up, the respectful way to refer to a black person was to call them “Colored.”