Yes bags but I know another reason (little devil emoticon might be appropriate here, I warn you).
After I left my ex, he cohabited for a while with a rather unpleasant social worker (she tried to push me down a flight of steps once - lovely). She wanted people to treat her as "black". One of her parents was what they used to call Anglo-Indian. But it was only if you knew that you might have noticed a slight olivey tint to her complexion. But it was, at the time, more PC to be black in certain circles.
Which is not to say that there are not some perfectly nice people of mixed race who choose a black identity because they think it is cooler (rather that wanting to be part of a downtrodden minority group) . And I have to say - more attractive colouring, fewer wrinkles, better musical heritage... As I was posting earlier on the cinema thread, look at Will Smith, mid 40s and only just starting to look like a grownup.