This is a 1950 Salesman order book, you can see that special color requests as Tim stated went through the zone office process. So a particular owner could then as now have it painted pretty much as desired. There is no ID plate or window sticker from the AD period that would designate the code other then the handwritten order form. I have never seen one of these other than the blanks as shown in picture two, if someone has an original that is filled out please post a picture.
https://www.flickr.com/photos/advance-design_parts_co/8335509814/in/set-72157631872034068
https://www.flickr.com/photos/advance-design_parts_co/8297889690/in/set-72157631872034068