From 1971 to the mid 1980s, the Cowboys' pants were always much bluer/darker on the back as opposed to the front. For whatever reason, they couldn't quite coordinate the colors. The pants in your photos were the ones they wore between 1971 and 1973, when they looked kinda charcoal gray. In 1974, they got significantly bluer.

Had no idea Red Fox was a team supplier. Always figured Southland Athletic took care of their uni needs.