Obviously, he's not just any dad. It's great that he is there supporting his son. But there is no reason for him to be wearing Texas garb. He's tacitly endorsing a direct competitor, if only for a night. That would be like Brett Favre showing up at the Packers/Cardinals game this weekend wearing Packers clothes.
I'm not saying he has to be wearing Gophers gear, but if he's not comfortable doing that, then wear normal, non-school clothing.
(P.S. I would have no problem with this if it were a D-IAA, DII, or DIII school where he was going to watch his son play. They are not competing for the same things we are.)