I’m quite sure that a white guy who for that day “identified as black” would have been welcomed with open arms.
Actually, any “people of color” who want to stand up against discrimination should do so as “identifying as white”.
In a manner of speaking, it would be as profound as “refusing to sit in the back of the bus”.
When confronted by it, and they would be, their response should be blunt:
“I do not obey bigots who want to bring back segregation.”