So here's the difference between saying "the blonde guy" and "the black guy" nowadays. People aren't stopped by the police for being blonde. Blondes haven't been systemically discriminated against for generations. There's no language close to calling someone blonde that is offensive.
I accept this is a very difficult distinction to make in the heat of the moment, but its basically the concept of a protected class: there are groups of people who have been, and continue to be subjected to, significant discrimination, so they are afforded increased protection. To me, this seems entirely reasonable, and the onus falls on those who are not in these groups to recognize this is not a problem we have and it isn't about us. Its not my place to comment on whether the coach should object to be being called "the black one".