A Jew named Christopher? I'm suprised no one's claiming he was black.
I am happy to say that has already happened.
I do not have a reference, but I am certain that I have seen that claim. More than once.
If he's Jewish they'll be able to tell. Some genetic researcher has traced several lines of Jewish DNA tracing back to the original tribes.
He can tell if a modern Jew named Cohen actually has DNA markers that track back to the tribe that was selected as the priests.