clothing. I wear one of two hats to every event even if they are not the right team. You can rep your own school's colors any time, anywhere. Also, they are CFB fans doing a CFB activity. Seems fine to rep the CFB team they actually root for. It is almost like the flairs they use on reddit. It lets you know where they stand and what they root for as context for any interaction.
I still think it's ok to tease them for doing this a bit.