Where did you get the data about, "All of the S-40-12 cars were delivered in yellow." ?
Or, "In 1958, the decision was made to paint NON-roller bearing stock cars freight car red so
only 'high speed' cars with roller bearings would be yellow." ?
The non-roller bearing S-40-12s were UP #46800 - 46999. Photos of that series are apparently scarce, but I have a photo of #46863D (Bob's Photo FUP20-A, San Diego, 4-'57) that is in FCR with a reweigh date of 10-55.
My spreadsheet also says those car sides were FCR, which agrees with UP drawing 303-C-10600, rev.A dated 6-12-50 (available at Colorado RR Museum).
The non-roller bearing S-40-13 class built in 1951-'52 also had FCR sides (Metcalfe book).
After a quick look, I can't find any NON-roller bearing UP stock cars painted with Armour Yellow sides.
Laguna Beach, CA