https://en.wikipedia.org/wiki/Fifth_Down_Game_(1940)
In this game, Cornell ran 4 plays, and ran their 4th down play believing it was indeed 4th down. For some unclear reason, the ref got confused and gave them an additional 4th down play. It was clear to both teams that play never should have happened and Dartmouth would have ran out the remaining 3 seconds. The blunder did not occur until after the 4th down play was run.
In the Colorado game, the error was made after 1st down and therefore affected all of the plays thereafter. Had the error not occurred, CU would have employed different play calling and the outcome of this alternate scenario is unclear.