So it's a tricky one, because I guess a lot of readers will default think characters are white or whatever their cultural norm is, and do need to have it pointed out somehow or other (in my defense, from the setting it was likely that all the characters would have white – most of them were). I think it's maybe better to have a more straightforward “X was black” approach, just stated by the narrator or POV character from the start, rather than all the subtle descriptive stuff (or food cliches) – especially as a lot of readers, like me, often skim read description. That's assuming that it isn't revealed from the dialogue or other aspects of the character, which would maybe be ideal – but people don't of course always speak or behave differently according to ethnicity.