In a 3-way tie between Kansas St., BYU, and Colorado, it's also KSU and BYU.
Now, if Iowa St. is undefeated and it's BYU and Colorado tied for 2nd, I'm not sure who wins the tiebreaker. Off the top of my head, BYU beating Kansas St. while Colorado lost to them may end up being the tiebreaker that gets BYU into the title game.