I haven't played Oakmont in 25 years (I used to play in The Swat) and I don't remember any of the brown fescue that some of your pictures show. It sort of gives the course a Shinnecock look where they've planted it although Oakmont is, most definitely, a parkland course.
While Oakmont has been renowned for it's ultra-fast greens even before everybody started stimping at 12+, it is a little known fact that all Pittsburgh courses have wonderful greens (e.g. Fox Chapel, the Field Club, Allegheny, etc.). Apparently, the city's location creates summer weather of hot days and cool nights - a superintendent's dream for firm and fast in and around the greens.