The Blue Car they released is an as delivered scheme, The Pullman cars actually had 3 pastel schemes, Blue, Magenta and Green. They also did a Cypress green schemes that weathered much better than the other three.
The letters designated different pool service as did the colors if I remember correctly although the colors may have originally beemn for specific manufacturer's... at least the 86' ers.
Also, the numbers may nopt neccessarily reflect a specifc AUTO parts plant. They used numbers to designate a bunch of specific customer assignments, like the Campbells Soup Plant in Napolean, although they didn't use large capacity boxcars there.