MLK wrote the letter January 18, 1966. The recipient was a man named William A. Bennett -- unclear who Bennett is. Dr. King embraced the term "dark skinned" ... saying he used it often as it reflects "both our great heritage and our devotion to a brand of Americanism of the highest order."

Of course, MLK has thoughts about the "n" word, which he says "carries with it a meaning deeply rooted in the debilitating racist caste ordering of our society's slavery epoch and segregation era."

The historical artifact was held in a private collection until recently, and now it's for sale on the Moments In Time site for $95,000.