If you're referring to DuBois' essay "On Being Ashamed of Oneself: An Essay on Race Pride," the themes are obviously race pride, and it is with regards to assimilation/a.k.a. national unity. It is a call to action. In the essay, DuBois begins talking about his grandfather, Alexander (1856) and the prejudice he faced, and how seventy years later, the African-American is still faced with insurmountable obstacles, especially with respect to high positions in industry and government. He talks about the importance of national unity, but warns that if it is passive assimilation, the African-American's quest for equality will be increasingly longer. In other words, as important as national unity is, DuBois makes the point that those of African descent cannot just assimilate and wait passively by for equality to slowly present itself.
"The next step, then, is certainly one on the part of the Negro and it involves group action."
He pretty much calls out the African community to organize in unity, be proud of their heritage, as it is as grand a heritage of any race. This is all very prescient. He seems to be hinting that once an organized African-American community peacefully obtains the same rights and privileges that whites enjoy, then and only then can we think about unimpeded national unity (at least with respect to racism) and any hope of "post-racism." He never actually uses the term "post-racism," but that is the ideal that he refers to.
I highly reccommend reading the essay. It's only about five pages long. Try google books: google "dubois race pride." It should direct you to W.E.B.Du Bois: A Reader. The essay's on page 76.