On TV it appeared to be a good 30-40% red.
Not even close. The visiting team at Iowa gets the first several rows next to the field on the visitors side at both ends of the field - so every time the Nebraska sideline is shown you would see a lot of red behind them unless they panned up higher into the stands. They did have an extra large group of Huskers in the north endzone, which is where several of the field goals were kicked/attempted, that would have been purchased from season ticket holders and then a section up in the corner at the SW where the students normally are but had turned in tickets due to school being out. Other than their alloted tickets and those two extra sections there were just some random Husker fans scattered throughout the stadium in greater numbers than normal but not to that extent.