Most definitive of all is the description of these FE-24 cars found in Frank Ellington and Joe Shine's book, Head End Cars, Volume One of the Santa Fe Railway Passenger Car Reference Series. The discussion is found on pages 138-141.
On page 140 is a b/w photo with the following description below it:
"Express Box Car 4224 (4100-4299) is shown at Los Angeles, January 14, 1968 in its final paint scheme, gray body with light gray lettering."
...and later, on page 141 near the end of the discussion of the history/equipment on these cars is the comment:
"In October 1961 cars to be repainted started receiving coach or Pullman green paint and Dulux yellow lettering with the big circle herald applied to the right of the doors, and "Ship and Travel Santa Fe All the Way" to the left above the reporting marks. Cars with roller bearings were painted overall dark gray with light grey lettering, a scheme which was applied to all box express cars after 1965. The cars lasted until the advent of Amtrak service in 1971; the final two cars were retired in 1980."
So, there you have it. No color photo, but what I would consider to be words from two of the most authoritative experts in the field on this road's history.
The Lionel car seems to fit the description quite well! I'd say it's as close to prototypical as I'd expect from this manufacturer.
IMHO, of course.
KD