The below photos are more for a reference point than a recommendation for a paint color shade. Top photo is one shared by Christopher2035 on the other big postwar dealer display thread. I like it because it shows both the grey-green-blue side color and the deeper green layout base color.
The second photo is of our layout. The control panel is Harrisburg green, which is recommended above. The layout is kelp forest, similar to the park picnic shared by John above.
In my opinion, Harrisburg green, while very close, needs a touch of blue to look more like the original. Kelp forest seems pretty close, and the Lionel 919 grass should also be applied to get the color and texture variation.
The other color you will need is the roadbed and road color. I haven’t seen a specific color posted for that, but it seems to be a shade of almond white.
i made the mistake of painting everything green first. You should paint everything the almond white base color, then lay track, tape it off, paint green in open spaces, and add lionel 919 grass to the wet green paint.
Your best bet for Lionel 919 grass is buy some on eBay.