Symbolism, Imagery, Allegory
This isn't exactly a symbol, but we're going to explain it briefly anyway because we have our explaining pants on. In regards to the ghetto Black lives in and the rest of the world, White tells Black:
"I don't get it. I mean, it's hopeless. This place is just a moral leper colony." (75)
Since leper colonies were places where people with leprosy were sent to live in isolation from the rest of society, a moral leper colony would be a place where immoral people were sent to live in isolation. White's suggesting that this world is merely a home for the bungled and botched—a cesspool of depravity. In doing so, though, there's the implication that everyone on earth has been separated from something moral—after all, you can only have a moral leper colony if there's some place else everyone's being kept away from.
It's a little crack in White's steadfast assertion that he has no faith. We'll let you decide how big of a deal it is, though, so go find your best thinking pants and get to it.