Can be used many ways.
I am black bred. Meaning the girl is pregnant by a black guy.
I have been black bred. Meaning the girl has been pregnant with a black bady and most likey will be again.
OMG i am going to be black bred meaning the girl is going to get pregnant by a black guy most likey if a girl uses it in this way she is going to be in a interracial gangbang, but can mean she is going to get pregnant by her black boyfriend.