Also, identifying as black can only ever mean apeing and copying in a basic way. You can dress, speak and act "black", but you can't change your ethnic origin in the same way you can have surgery to change your sex.
Your ancestry is your ancestry and with the best will in the world it cannot be changed.
Saying that, a PP is right to ask how far back we go to determine ethnic origin.
Nationality and culture are so fluid. I'm Brit but live abroad. I lived in the UK my entire childhood and identify as British. Actually I'm a quarter Latvian but as I don't speak the language or know anything about the culture I ignore it.
My child has dual nationality. He is growing up with a British childhood and British influences in a country which isn't Britain. So he isn't fully a part of his home country but neither is he having the full British experience. He will grow up to be an odd mix of the two and what he identifies with will be entirely about how he feels.
Added to this, I have friends with third culture kids who have two different heritage countries from the parents but are growing up in a third culture which is alien to both parents. They speak all three languages and identify with all three cultures. What nationality are they? It's an interesting but ultimately pointless question - they are whatever they feel.