I thought during the non conference that the visiting team brought their officials. But I noticed the Michigan State game was BIG officiating crew and the cu/CSU game is pac12 officials and sCUm is the home team at neutral site.
There's no rule that states which conference's officials are used. Which conference's officials are used at which game is likely specified in the contract the two teams agree on for the game. I think we've had home and away series where our conference's officials were used at both games.