When we decided to paint the train green back in the mid-1980's we got went to a Dupont paint dealer in ABQ and asked if they had any historic color samples in their files. Amazingly they did. They came up with a handful of samples of "Pullman Green", mixed up some sample pint cans and off we went to see what we liked. The samples varied quite a bit from almost brown to forest green. We picked what we thought was the best color and away we went. Originally we used oil-based enamel, either Centauri or Dulux. Which lasted fairly well. Then they invented the water-based enamel that everyone uses nowadays. It didn't last anywhere near as long.
FYI, back then the cars were segregated with the flat tops on the east side and clerestory roofed cars on the west end. My idea was paint the Antonito train red and the Chama train green. Back then most passengers rode to Osier and back. We could simply tell passengers to "get on the RED train" or get on the GREEN train"....
Obviously didn't happen.