Apropos the recent question here about what color to use to represent the wood decks of flatcars, it seems worth mentioning something that I think is a good general principle of color selection for things model railroad, and I'd like to get some comments. (Disclaimer: I certainly don't claim to be an expert scenicker or anything, but I know a couple things about what works in that area.)
The principle is this, and it's pretty simple: keep it light. The normal tendency is to paint things the colors they are "in real life", which ends up being much too dark in the context of a model railroad. Like things like time and speed, color also seems to need to be "scaled" somewhat in order to make it believable.
Of course, there are lots of factors here: viewing distance, type and brightness of illumination, etc. But I think this general principle still holds.
A few years before the magazine went out of print, Bob Hundman ran an interesting series of articles in his /Mainline Modeler/ on the theme "Where's the Black?", where he pointed out that objects that we normally think of as black, like heavily weathered steam locomotives, are really never black at all. He demonstrated this with some painted models, and sure enough, when the paint was several shades lighter than "black", the models were much more believable.
I think this principle is evident when you look at scenes by, say, George Sellios, and examine his colors carefully. I haven't seen any good color photos of John Allen's work, but I'm guessing the same was true for it as well.