Painting Western Scale Models Machinery

[TRAINS1941]

Help or maybe Chuck this is up your alley.
Have the machinery for a machine shop plus all the bid equipment Planer, Drill Press, Sheel Puller Wheel Borer, etc.
Have been playing with a Model Master Paints Ghost Gray with a little white and brown added to it for a cokor for the machines.  Not bad but would like to know does anybody else have any suggestions on a paint color.  Or maybe even a green of sorts.

Thanks

Jerry