Octavia E. Butler

People who think about time travel stories sometimes think that going back in time would be fun because you would have all the information you needed to be much more astute than the people there, when the truth is of course you wouldn't.

The norm is white, apparently, in the view of people who see things in that way. For them, the only reason you would introduce a black character is to introduce this kind of abnormality. Usually, it's because you're telling a story about racism or at least about race.