Advice sought. Singling someone out by ref to ethnicity

[FizzyLaser]

Hi all.
asking this as a student I teach asked what the state of play with this.
imagine a range of people:women with brown hair say a shop or similar situation, and one of them is black and you’re trying to indicate that it’s the black person who is assisting you they’re all in staff uniform.
is it ok to use ethnicity (white or black or Asian I suppose) to describe appearance

yes

I guess. Normally people might introduce themselves by name in a shop so I'd ask that first. But if they were to forget, and that's the only distinguishing characteristic, then it would be ok. It's not being used to offend

Yes

No.

Yes.

Yes, but only if it's the only way to identify them.