In other words, black is whatever we say it is

[…] Consider this: Just 40 years ago, one could make certain
assumptions about the average Negro, or black American. She
was probably no more than one generation removed from the
South; whether a Northerner or Southerner, he had first-hand
knowledge of Jim Crow, or segregation; when it came to
religion, he or she was most likely Protestant.
But scholars like Vernellia Randal, a law professor at the
University of Dayton, point out that those assumptions have
fallen in the face of urbanization, migration and
integration. […]

Afi-Odelia Scruggs' Cleveland Plain Dealer op-ed "Obama's identity crisis"

[…] "I think it could very well be generational—that people like myself,
who are older and more established and have these relationships, will
stay with the people that we know. Whereas younger people, who don’t
have these relationships, will say that this fellow seems to be an
outsider too—and so, therefore, they are attracted to him." […]

Ex-New York State Comptroller Carl McCall, quoted in Jason Horowitz's New York Observer article "Clinton, Obama Vying for Black Power-Brokers"

Update:

[…] According to Census Bureau figures, in 2004, African-Americans cast
14 million votes nationwide. Now comes this stunner: Because
African-American men not only are fewer in number but also register and
vote at much lower rates, black women cast almost three of every five
of these votes – 59 percent, to be precise. White women also outnumber,
out-register and outvote white men, but the disparity is smaller (53
percent to 47 percent). […]

[…] Senator Obama's allure may be perceived as more
generationally prospective, whereas the appeal of Senator Clinton – the
former first lady married to the man novelist Toni Morrison once called
the "first black president" – is deemed more historically
retrospective. "He brings a lot to our heritage and culture, especially
to our youth," said Victoria Haynes, a 47-year-old Denver native who
worked on the campaign of newly elected Colorado Gov. Bill Ritter Jr.
"She brings a lot of strength as a woman who came from behind her
husband to lead as a woman." […]

Thomas F. Schaller's Baltimore Sun op-ed "Black women face dilemma in Democratic primary"