Caveat: Negotiations are just starting.

Negotiations with both roads are in the earliest stages. The 315 group will use what equipment the respective companies are able to assign us, green, yellow red, whatever. It is a distinct possibility that the 315 will be operating during Railfest. It is also a strong possibility that 315 will spend part of next summer on the C&TS. All this depends on how well 315 performs in tests, whether or not it needs big repairs to keep running, and, of course, the success of negotiations with both roads.
I know that Jeff Ellingson (painter for the D&SNG) had done an incredible job last year repainting 478 as 472, with green jacket and late 1930s lettering, perhaps the most beautiful paint job I ever saw on a steam engine. There was some talk this summer of repainting a couple of "heritage" cars on the D&S green, but I never saw them.
It's important to emphasize that it is a good thing that historic locomotives return to the rails, whether or not the train is a replica of a 1930s era consist. That locomotives returning to operation for the first time in decades will have mechanical problems major or minor, is also something to expect.