The thesis that anchors the story is that individuality is a basic human right to society, and a human obligation to one self- Racism opresses the individuality of those who are targeted. Therefore, racism is not just preferencial treatment of one race versus another: It is an sentiment that infuses through society with the potential of capturing it, and with the capability of breaking with every canon of humanity ever established in history, to the point of making an entire race, culture or creed seem and feel "invisible" in the eyes of the majority.
Not only did the story display racism from whites to blacks, but also the superiority complex of whites who felt that they were giving amazing favors to the protagonist. Not only is he now racially invisible, but also socially invisible-- and powerless.
Finally, the story also portrays the thesis intra-racial stereotyping: The grandmother asking the nameless narrator to act more like a "black folk" and exaggerate his black mannerisms to be in good terms with his white employer. The college professor suggesting that, on the contrary, let's act more like whites to "be more accepted"- All these are signs of stereotypical cultural expectation.
Hence, throughout the story these are the two main elements: a Racism and stereotyping, b) the battle against a reductionist society, c) the loss of the sense of self.