What do you get when you mix black and white? Grey, you get grey.
Not 'bi-racial', not 'mixed race', not 'swirled'. Where were you the day tertiary colours were taught at school? There, but not listening most likely.
This is not a test any one should fail.
Black + White = Grey.
P.S. 'Bi-racial' sounds like a chess board, and 'mixed-race' sounds like they couldn't make up their mind.