I got the Scalecoat GN Green from reading an article in the Timber Transfer that said it was a near perfect match for EBT's coach green. That's the good news. The downside is that Scalecoat isn't acrylic. It is, however, available in spray, which is a good thing when painting something as large as a 1:20 passenger car.
Here's the same color, weathered and faded a little bit.
If you must use acrylics, try Badger ModelFlex BNSF Green. I've not compared them side-by-side, but from the BNSF locos that run through Denver, I'd bet its pretty close, though maybe a little more on the "green" than "olive" side of things. One thing you could do is buy a jar of Scalecoat paint, and take it to your local paint store and have them mix you a pint of latex to match.
BTW,
Shawmut Car Shops has my East Broad Top passenger car lettering artwork, and can cut you vinyl lettering for your cars, or print you decals should you prefer. I've found the vinyl looks great. (The baggage car has vinyl lettering.)
For the interiors, it depends on the car. Some cars were painted, others had stained wood panels. Iron Horse Engraving offers the miners' coach, combine, and baggage car; I'm almost positive they were painted (especially the miner's coach).
For this, I just found a suitable light green bottle of acrylic craft paint (Folk Art, or similar) from the craft store. Krylon makes a good light green in a spray can, which is what I used on my Iron Horse Engraving cars. It's a shade darker than what's in these photos, but still a good light green.
Later,
K