From what I understand, the slave owners classified anyone with black parentage, even if not 100%, as "black", therefore Obama calling himself black, is only following a precedent.
Same could be said of Halle Berry, who despite her occasional whinges is clearly not black.
Maybe this is more an American thing though. I'd say a huge proportion of the UK has Irish ancestry in them, but you don't see many painting themselves green on St Paddys day. Contrast this with America
