"But Black people have never been nonexistent, or invisible, in the white sitcom."

"They have been invisible only in the way that Black people who service the margins of white world-making must be. In a genre whose conventions (and hilarity) thrive on white ridiculousness, Black people, relegated to the smallest of parts, exist to rein in the free play of whites, reminding viewers how safely deviant the main cast can be.... Black people on Seinfeld play a very particular role, defining the social edges of 'very,' or too much.... All the bombast, wackiness, and camp belong in the domain of the four protagonists — Jerry, George, Elaine, and Kramer, plus a rotating circle of co-conspirators.... [T]he group is selfish and deranged, delicious micromenaces to normalcy and etiquette who nonetheless enter and leave each episode with their worlds intact. When white characters run wild on Seinfeld, Black people are cops. They exist as agents of public decency next to whom our main characters appear all the more indecent.... Friends, the sitcom most frequently judged for its lack of black characters, stations its black actors on the mundane edges of urban life.... [B]lack characters play a significant role precisely because they are true strangers — estranged by city planning and the color line — for these main casts to bump up against...."

From "When Black People Appear on Seinfeld" by Lauren Michele Jackson (New York Magazine).

Example of what the author is talking about: