Beauty is indeed in the eye of the beholder. Much of one's taste is affected by what the culture throws at you, and regardless, it is not voluntary, any more than a taste for vanilla versus strawberry.
How many black females do you see in porn? Very, very few, and the ones that you do see are "blacks" with straight hair, blue eyes, and other Caucasian traits inherited from non-blacks in their genetic background. If the general population found black women to be beautiful or sexy, they would be port stars.
Black-blacks - Roberta Flack, Serena Williams, and so on, are simply not considered by the major culture to be pretty.
Even if this kid wasn't joking (and I maintain that he was not), it is outrageous that the school is punishing him for expressing his opinion.
Again, the delicate snowflakes of academe are winning the war to control America's campuses. What conceivable value can this kabuki dance have for one's education or future?