Varnish is a nickname for passenger equipment for a reason, it shined. Color and finish is a really touchy subject, and straight gloss looks bad for other reasons, mainly because reflections and surface finish don't scale down well in the layout room. My own preference is a nice semi-gloss to satin finish on passenger equipment. Save the dead flat for the freight cars as it just doesn't have the right look for passenger equipment in revenue service.
I've never liked the MTL rendition of Pullman Green either. I think it first jumped out on the Troop cars in N scale, which were flat and very light in color. It sorta matches the Pollyscale Pullman Green, but I feel that shade is off and too light as well, so not a good reference. MTL doesn't use Pollyscale, they get their paint custom mixed from a California company that also makes the Accuflex/Modelflex lines. You can send the company paint chips and have them matched to a batch of paint special, but that doesn't mean they match the tints correctly either. I'd like to know what chips MTL sends in... Joe mentioned that the UP colors were derived from official UP paint chips or something, but either the colors weren't matched by a good eye, or they weren't the right era paint chip, as the MTL UP passenger car colors are off also. Again, my opinion.
I've heard people say that the GN Empire Builder green was Pullman green, but I always treat it as a dark green with less olive. My favorite rendition has probably been the ConCor updated release of Empire Builder cars in N scale, back in the mid-90's (?) when they started painting the dome window sashes on the clear dome roof. Walther's recently released the train in HO, and while the green is generally in the ball park, the orange seems to be too saturated. Anyway, I'm not a fan of the MTL color choice, which was your question in the first place.
On the decals, I like that idea.