I don't think the problem is with black women holding out for black men; rather it's with blacks (especially black women) being considered undesirable. OKCupid crunched the data for its online dating service and came up with some surprising conclusions, among them being that black women are far more likely to reply when men send them messages than women of other races and far less likely to get replied to when they send messages to men, and that although black women reply to black men (and black men reply to black women) more than any other race does, blacks appear to reply more to non-blacks than to other blacks:
How Your Race Affects The Messages You Get OkTrends
The data are less clear when it comes to homosexual matchups, however:
Same-Sex Data for Race vs. Reply Rates OkTrends
This is all after controlling for such factors as attractiveness (as determined by the userbase) and despite the stated preferences of the users and the trend of OKCupid users being younger, more intelligent, and more progressive than the general American population.
Also, in case this has any relevance, white men are significantly more likely to get replied to, regardless of the race of the women they message, and Middle Eastern women are more likely to get replied to overall.
Remember, the data separated the factor of race from numerous other important factors; a highly attractive woman is likely to get replied to regardless of her race, but the moderately attractive ones (which turn out to be the vast majority, unlike the men, who were mostly rated unattractive) are more likely to have problems based on their race.
Then again, for all I know it could be that OKCupid users are far more likely to look outside their own race than the general population, and maybe the typical black woman really is holding out for a black man...