Can't explain the difference in the roof color (black vs. silver) but I think there may be a problem in the online rendering of the orange/crimson color scheme - which is not unique to Lionel catalogs.
The true colors are in fact close to the livery of the Chicago South Shore and South Bend, and I recall that years ago MTH cataloged a set of interurbans that the catalog depicted like this:
The body color shown is all wrong and I don't believe that the set was actually produced to look like this (I passed on it).
The New Lionel RPO car looks a lot like the MTH Madison cars that have been produced in various liveries for years, including Milwaukee Road and South Shore. For the former the catalog image (Railking) looks like this:
which is again not quite right and the cars as produced came out much more like the current Lionel product. I don't have a picture of these but again the orange is more like that used for South Shore Madisons (not my layout but I do have all of these cars):
I know that there's likely a technical difference between the orange used by the Milwaukee Road and the South Shore but the difference as rendered in most models is not obvious.
I can't find a single photo of a Milwaukee Road Madison RPO car as rendered by Lionel and I wonder if, like the MTH South Shore cars, this is essentially a fantasy scheme? The one existing Milwaukee Road car described as an RPO (although configured for baggage) I have found is a streamliner and looks like this:
Overall the similarity between the Lionel RPO and the various MTH Madison cars is strong (right down to the rivets!) and my guess is that the Lionel catalog illustration was no more accurate than some of the MTH ones.
P.S. Just looked at the current Lionel online image of their car and it looks like the body color has been changed in it although the roof color is still black: