Keep in mind that while you can and will see variations in some colors during World War II, that the Target Colors were the same. Anyone that doesn't know what Target Color they are aiming for has zero chance of re-creating a scene from World War II that they might see in a photo.
There are actually modelers out there that can paint a model to match the fine points of getting the variations right on a vehicle or aircraft that has such "unmatched" areas visible in photos. When we talk about paint standards, that is only so that any given modeler has a place to start,,,,,,since in the case of OD, there are about 400 model paints that are "Green", but are surely not a good place to start with in the pursuit of painting a Sherman.
Such as getting the two different Light Gull Grays right in order to build the middle aircraft on this decal sheet www.modelingmadness.com/.../am72186.htm This might be a poor example, since it is a case of the standard changing, which changed the colors, not "weathering" or "the impossiblity of manufacturing paint" (yes, this is based on a real photo, I have a copy of it)
Just throwing this out there for any reader that finds this thread later and thinks that there was never even any attempt to ever match a color,,,,,,,,,,,,,,,,, or never any paint delivered via ship to a war zone, etc,,,,,,,,when in fact, due to subs sinking ships, sometimes the ships with the paint got through and the ones with the tires didn't (pick any two war items for this example) Paints, the standards, brushes, air guns, hoses, compressors, etc, etc, were all part of the "squadron kit" of equipment and supplies that went with a unit when they deployed from place to place, unless it was a TDY (and even then, there was a list of things that "Had" to go along)
I got my second copy of the Federal Standard from the file cabinets of a USMC unit, they were headed for the trash when a new, updated edition came out, and the Gunny let those of us that were modelers pick the sets out before it went into the barrell. (yes, "sets", as in multiple)
Rex