I did a search but could find nothing conclusive - is there a specific time period or car series for the UP change from FCR to yellow for stock cars?
The UP first painted stock cars yellow (with aluminum roof and ends) in early 1947, when they inaugurated a fast livestock service between Salt Lake and Los Angeles. The paint scheme was ONLY for the cars in that service,which had been equipped with roller-bearing trucks. All other stock car remained BCR. Gradually more and more of the BCR cars received aluminum roofs.
AFAIK this pattern of paint assignment remained through the 1950s. Others on this list can doubtless stay more.
