It's common knowledge that at least during WWII many aircraft builders differed in the paint colors that they used on their planes as they left the factory. Although the paint properties were known the suppliers of the ingredients differed. So you would have OD of a little different shade and hue comming out of different factories. I'm sure the same situation existed during WWI as well. The translation of a written requirement and the application of that requirement can and does vary widely depending on lots of variables.
Going back to the original postulate I believe the intent was that regardless of the correct color our Preception of that color can and does change. When it comes to Judging, perception is everything, almost.