I know about the A&WP silver cars, Seaboard had some grey and some green, and the GM&O had some brighter red cars with the winged logo. I don’t know if the CofG oval design cars (think Lionel) fit in for that timeframe. Others, anyone? (ACL, Clinchfield, FEC, L&N, NC&StL, TAG, perhaps?)
This might actually be better answered on the Prototype information for the modeler forum.
Tom