Those covers were largely generic covers. I wouldn't put any stock into those images.
In 1933, a newspaper article reported ISU would continue to wear their blue jerseys (started in 1931), but needed to wear red jerseys for two games that season against other teams that were wearing either blue or black. For the 1933 season, ISU's helmets were changing from all black to black and tan.
I don't immediately have files for the late '30s, since that's a bit removed from Jack Trice's time. It's important to note that the film used at that time was panchromatic (see:
The yellow lipstick of Jack Trice story) and color reproduction is somewhat easier to guess.
Looking at your photo, seems pretty obvious it is a two-tone helmet. My immediate feeling, based on years of research into this area, is a light brown and tan combo of dyed leather, as leather helmets were not painted.
It could easily be a different color combo. Perhaps yellow and tan. Reporting on uniform changes was pretty spotty in those days and I would need to dedicate a bunch of time that I don't have to truly nail it down.
For example, I notice there are three vent holes per "vertical column" on the helmets and in my experience, only two holes was the far more common iteration, thus looking though equipment catalogs of the era should yield the manufacturer, and thus possible color combos.
BTW, here's film from that very Northwestern vs. Iowa State game, featuring NW's black player returning a KO for a TD:
https://media.northwestern.edu/media_objects/s7526c54p
