Colorado and Nebraska were old Big 8/12 rivals. They paused because they split but it is very much still a rivalry.
I'm a Colorado football fan. The Colorado-Nebraska rivalry was created. They weren't "natural" rivals... Nebraska was a national power, and really didn't "care" about Colorado.
Nebraska and Oklahoma were the powers of the Big Eight, and everyone else was just kinda there... It wasn't like a Kansas-Mizzou situation...
Colorado just started printing schedules for fans in the late 80s that had the Nebraska game in red. If we want to be good, that's the game we have to win. And Colorado got good in the 90s. Nebraska was the biggest game of the year... Nebraska did not feel the same way... their biggest game of they year was their obstacle in the path to a championship.
Colorado actually became a title contender was the only reason the game meant something. It was THE GAME to Colorado. to Nebraska, it was just another obstacle; no different than if K-State or Iowa State was good that year.
A real rivalry is when no one gives a damn about records or standings, you just hate the other team so much that "If we go 1-11, the one win better be..." kind of thing. Like Army-Navy. THAT is the best rivalry in sports, solely because they care far less about anything other than beating each other.
There have been ZERO STAKES in the championship landscape to Army-Navy in like 60 years, and neither of them care a single iota. Their season is DEFINED by who wins that game. If you offered them "11-1 but you lose to Army/Navy vs 1-11 but you beat Army/Navy" they'd HAVE TO THINK HARD about it.
If Nebraska had to pick between 11-1, loss to Colorado vs 1-11 win over Colorado, they're 100% picking 11-1 every single person, every single time. (Army/Navy, it would be an interesting poll).