Well, Akon is straight from West Africa, so there is a chance that he is not mixed.
I really don't completely understand your question but I do know that Blacks in America are black under the U.S. definition, but if you go to parts of Africa where all the people are straight-up black or very dark skinned, than they will think of us more as "mixed" instead of black. (Which is what we are, because many black people mixed with whites and some mixed with natives, so "African Americans" are a mixed race ethnic group.)