Washington coaches had to restrain the team's only senior, who walked up to the student before slapping him after the halftime buzzer sounded.
"I'm aware of it," Huskies coach Lorenzo Romar said. "I don't know anything about the details. I will look into it."
A Pac-12 spokesperson said Friday the conference is reviewing the incident.
Dime, who is from Dakar, Senegal, was sitting out his ninth consecutive game with a broken right pinkie.
The Tacoma News Tribune reported a man in the Colorado student section said Dime slapped him but gave his name only as Brian.
The man said he did not want to comment further, other than to say "everything's been made right," the News Tribune reported.
Information from The Associated Press was used in this report.