I just started reading DFW's The Broom of the System and there's a paragraph at the beginning of chapter three that sets the scene. It's filled with seemingly trivial details about the color of paint on handrails (yellow) and the texture of the lawn grass. Embedded in there is this: "Outside the doors an old black woman stood motionless with her walker, her mouth open to the sun." Evocative, yes. But the generic "old black woman" kind of bothers me. If he was describing an old white woman he presumably would have just written, "old woman." Or at least he would have been more specific in his description of skin tone. This is presumably because of some innate bias we have when imagining fictional characters to thinking of them as similar to ourselves by default. So for DFW, who was a white male, in order to paint the picture he imagined, he had to note that this old woman was black.
What I'm getting at is that by noting specifically that the woman is black it underscores the fact that this detail is a real point of distinction and that since none of the other characters so far have been described as black, we assume that they aren't and we can probably continue to make this same assumption for the rest of the novel. It makes me wonder what a black reader might think when arriving at this line.
While I imagine that Wallace did not exactly have a black audience in mind when he wrote the book, I also can't assume that he only imagined white people reading his work.