The cars in question appear to be painted standard freight car red with white lettering. In my knowledge no one has come up with the official reasoning for doing this. At the time this was done there were still quite a few passenger cars up on the 3rd division. They appear to have run several specials for the CCC and other outfits. One CCC special ran out on the RGS. I could not tell you if the red cars were on this train or not. I can't think of a reason to paint them red for CCC use. It has also been suggested the cars were painted for use as drover's cars on stock trains. No pics seem to exist of the red cars in actual use.
It seems that combine 215 was painted red for a while when it equipped with the cupola.