Bob Johnson's comments, as coordinator of the archives of the PRRT&HS:
a - As built the cars were painted with Tuscan Red body, Metallic Brown roof, Olive trucks and underbody equipment, Black handholds and ironwork (underframe and sill steps), and Gold Leaf lettering edged with a 1/16" Black line. Side lettering included a 6" high "PENNSYLVANIA", 6" car number with figures spaced 1 1/2" apart, 4" high "AMERICAN RAILWAY EXPRESS", and 4" high "REFRIGERATOR". End lettering was 4" high "P.R.R." and car number. Lettering style was the older Block Type with coved letters "P", "S", "R", "C" and "G".
b - On 4-4-1929 "AMERICAN RAILWAY EXPRESS" was changed to "RAILWAY EXPRESS AGENCY, INC." It's possible that the last few cars built received this lettering as built. I haven't seen any photos showing this style.
c - On 10-15-1929 the lettering was simplified to "RAILWAY EXPRESS AGENCY".
d - On 8-14-1930 the end numbers were removed.
e - On 10-21-1930 the side numerals were spaced 2 3/8" apart and the 4" lettering was spaced wider.
f - On 7-9-1936 the lettering was changed from Gold Leaf to Buff Lettering Color, still edged with Black. I believe this is Walthers 5881 (below), "prewar", except I'm not sure about the black edging.
g - On 4-12-1938 the lettering was changed from Block Type to Futura. However, I have never seen a photo of a Futura R50B. In fact, official photos of a freshly painted R50B taken on 9-24-1938 show Block Type.
h - On 4-17-1939 the Black edging of the letters and numerals was dropped. Walthers 5884 (below), "1939 scheme".
i - On 7-13-1939 the roof paint was changed from Metallic Brown to Car Cement (a dull black).
j1 - On 6-13-1941 the lettering style was changed back to Block Type and the spacing of the numerals was increases to 5 5/8".
j2 - On 9-29-1943 the trucks were changed from Olive to Black and the underframe and equipment below the body were changed from Olive to Tuscan Red. Walthers 5885 (below), "Tuscan scheme '43-44".
k - On 9-7-1944 the paint color for the trucks was changed from Black to Truck Green Enamel and all equipment below the car body was changed from Tuscan Red to Truck Green Enamel.
l - On 5-25-1945 the paint color for trucks and all underbody equipment was changed from Truck Green Enamel to Black.
m - On 8-1-1945 the 6" letters "P" and "S" were changed from the older cove style to a rounded Block Type. It's likely that the 4" letters also changed from cove style to rounded at the same time. Walthers 5882 (below), postwar.
n - On 2-15-1954 the lettering "RAILWAY EXPRESS AGENCY" was crossed off and no longer applied to cars. Walthers 5886 (below), "No REA logo, 1954".
o - In 1962 Scotchlite reflective keystones began to be applied to passenger cars. When this was done, no road name was used. I have no photos of this style on an R50B. Walthers 5883 (below).
p - At the beginning of 1967 there were only six R50B cars left on the passenger equipment roster. All were gone from the roster by the end of 1967. Thus, it's unlikely that any were lettered for Penn Central.