Tom, The colors I am always interested in are the oxide reds, faded greens (gray green vice dark green), and then the depot buff colors. Of course I still ask myself were these available colors for my time period and local? Paints were different in the 20s and 30s, and I suspect (remember I am suspecting) that the further west from the east coast you tended to get limited colors right down to white wash. Henry Ford said you can have any color as long as it was black...I think research is appropriate, but I don't know where to start other than googling "what colors of exterior paints were available for the 19XX"
As Les mentioned, the Barn reds are probably the most common if buildings were painted. White lead was a common color too. The buildings at Rayonier's Railroad Camp (at least in the 50's and up) were a kind of Mineral Red. I also like green and the buff colors-I'm sure you could eventually find a prototype for most any color.
The most common pigment for white was lead oxide: http://en.wikipedia.org/wiki/Lead_paint And that's the same pigment that can make an historic house into a Superfund site :-( However, lead white paint lasts a long time, which is one reason why it was so common.
Tom, I copied this one from one of our members some time back, can't remember who. But this was the notes I took from him for this color. Where it says "I" it would be "He". Any way I like the way he did this color choice. I distressed and added grain to the boards, battens and then started the coloring process: 1. A wash of Acrylic Barn Red the red under tone color of a worn and faded wall 2. Burnt Umber weathering powder 3. Wash of A&I 4. Dry Brushing with the following colors: Goose feather ( light tan) Country Twill ( Light brown) Black for the lower board stains Country Twill again At this point, Iím completely satisfied with how the first two walls look.