"in many cases lack black blood"

When you think of it that's a really strange expression, "black blood" - picking on what is perhaps the most evident human characteristic where it undeniable that colour differences just don't exist.
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Curuiously enough Black people in England are much more liable to refer to themselves as "Black British" rather than "Black English" - I suspect that's largely becuase of the alliteration. Over the border in Scotland my impression is that they are more likely to say they are Black Scottish rather than Black British.