On the PRR, the graphite treatment of smokeboxes and firebox sides were generally consistent within a shop facility, but varied between shop facilities. For example, Columbus might use a lighter graphite mix than Altoona.
Regarding the above linked photos:
"Smoke box silver?" is Baldwin's builder's photo. For these photos, driver tires were usually painted white (and usually only on the side facing the camera) and smokeboxes had a gray treatment. These photos were often retouched as well.
"Smoke box color 2" shows the S2 posed on Horseshoe Curve. I've read that this was only done during its first trip west after being built. Thus the smokebox in this photo had the graphite applied by Baldwin. The S2 never ran east of Pittsburgh, and almost exclusively served the Crestline, OH to Chicago segment of the railroad, as did the S1. The nickname for this mostly flat and straight segment was "the race track."
The lighting in "Smoke box color 3" is so bad that no conclusion should be drawn from the photo.
This leaves the "Smoke box color" photo, taken in 1950 (thus after PRR shopping) and also taken in direct sunlight. Dark graphite wins the day!