There is a pretty large file at the Colo RR Museum on the UP stock car rebuild from box cars that took place at Denver shops. Will check it out to see what there is on paint colors.
The question should have been when did the UP begin painting their stock cars Armour Yellow rather than a general request regarding other freight equipment. The person who put the question to me models in the late 1940s."
Vol 1,#1 of the "Streamliner" sez the stock car conversion for the Livestock Dispatch service occurred in 1947. Aluminum roof and ends, yellow sides, black underbody and trucks. Not all stock cars were converted for this service so a significant quantity stayed in the red scheme.
