"The vote which is open to being questioned, is the black vote." Presumably the implication is that it was all about "black" people voting for a "black" candidate?

On what grounds? In 2008 the "black vote" was indeed 95% for Obama to to 4% for McCain.   But in 2004 it was 89% for Kerry and 11% for McCain.

In comparison the "white vote" (meaning the non-Hispanic "white" vote
was 43% for Obama as against 55% for McCain - compared to 2008 when it was 42% for Kerry against 57% for Bush.

For both sets of voters the proportional vote for the Democrat went up a few points, and the vote for the Republican went down. And both times it was clear that "black voters" are consistently, at this time anyway, more likely to vote Democrat than white voters are - whatever the colour of the candidate in question.