People are also more racist than normal when their assets are on the line (aka paranoia).
Research shows that if a neighborhood is "becoming more black" or "becoming more white", that has implications for property valuation. (Yes, this comes from racism, in case you were wondering.)
Who wants to be the guinea pig to wager the value of his house on diversity? (... and it's fine if you do, just be aware that it has implications)
It's an advantage for wealthy, educated blacks to live in mostly white neighborhoods, because it shows that they've "made it" according to the (admittedly racist) standards of success.
And it's an advantage for the white majority in such a neighborhood to have a few blacks around to demonstrate how incredibly non-racist they are.
(Obviously, the underclass (of whatever race) gets left out to dry.)
Generally, a poor neighborhood is a good place to be from, to contrast with present circumstances and look at how far you've come. It's not a good place to be.
I live in mostly white neighborhoods because that's where I and my family wanted to live.
It was not to show that we had "made" it or to give the neighbors the opportunity to demonstrate their lack of racism. I think, far too often, people focus on race and don't realize that class distinctions are frequently better indicators.
On that basis, it seems quite reasonable to choose to live amongst people who are similar to me and not amongst those who aren't.
As it turns out, I'm now in South Africa and it's easier to see my point. Most of my neighbors are black or "colored" but I live near them because it's a nice neighborhood and not becuase of their race.