A South African university is investigating white students accused of racism for wearing dark coloring on their faces in a portrayal of Venus and Serena Williams at a costume party.

Stellenbosch University said Thursday that it was informed about a photograph on Twitter that showed two students posing as the tennis siblings. It noted social media reaction that mentioned "blackface," which was common in old American minstrel shows featuring white performers as stereotyped black characters.

The two students and another student who posted the photograph say they aimed to portray two sports stars without "malicious or racial intent," and they regret their judgment error.

The student council says some students believe the three should be expelled, while others dismiss the incident as a mistake that should not be taken seriously.