Maybe 80% at best wear blue (omitting white out games). Still too many fans wearing white, black, random colors with nothing to do with BYU; and my perennial favorite is the handful in red but cheer so unlikely they're ute fans. And that doesn't include those wearing their free tshirt from the "BYU bib" era that's so faded it's barely blue and has more holes than Swiss cheese.
I haven't missed a home game in 15yrs and while it's improved, we still have a long way to go