If you want to pull the NPC "reindeer" cars, I'd paint it in a NYC "lightning stripe" scheme kind of like a combination of the schemes on the photos I've linked to on the railpictures.net web site:
The first photo is a NYC P2a in the "lightning stripe" scheme.
The second photo is a NYC F3 in the "lightning stripe" scheme.
The third photo is a PRR GG1 in the 5 stripe scheme.
I'd do a lightning stripe kind of like the NYC F3, but double ended like on the P2a. The "NORTH POLE CENTRAL" lettering and engine numbers would below the stripe. The NPC logo would be on both ends in the same location as the PRR keystone on the GG1. You could add a NPC logo on either side at the center of the locomotive above the lightning stripe like the PRR keystone on the GG1.
The locomotive color would be red to match the passenger cars, and the "lightning stripe" would be green to match the passenger car. Lettering and numbers would be white.