Colo Rail Annual 25 says a 50/50 mix of tuscan red and caboose red for pre 1912. with a minerrl brown roof & trucks (= dark brown).
For the coach red a dark red oxide is fairly close - Jack Thompson has a freelance railroad and say his color is 'Pennsy Maroon' (Tuscan Red) so the DRG red would be a bit lighter.
Goto the following link for his re-paints of the AMS coaches but note they are 'weathered'
the last one less so.
http://4largescale.com/Thompson/56.htm
A PRR GG1 in new condition (tuscan) is at
http://www.trainweb.org/railpix/miscpix/PRR_GG1ac4877-4-24-82.jpg < Link To http://www.trainweb.org/r..._GG1ac4877-4-24-82.jpg
A final thought is to take the coach you want to match to a car paint mixer who should be able to match it for you; ensure it is acrylic paint and can be painted onto plastic.
Yours Peter.