We have the longest series with Minnesota, 51 games. They own a 28-21-2 series lead, but we have won the last 14 games dating back to the start of the Bob Devaney era. And from 1969 on, 10 games, the scores were lopsided in favor of Big Red.
As far as replacing Colorado goes, well, I don't think anybody ever goes in search of such an opponent. It would require a team to "circle Nebraska on the schedule", pump out continued hype about how they are going to beat Nebraska even if its week one and they play us in week 9, require their scout team to dawn Husker jerseys the week they play us, and to claim on a unilateral basis that Nebraska is their new rival.
What Big Ten team is going to do all that? Let us hope the answer to that is...NONE
But the Buffs have already replaced us by targeting Utah as their "new rival". Have fun with that Utah.