Color photography was in its infancy during WW2. Keep that in mind. Photography is a balance of exposures and stopping that exposure at a certain time limit. Not just once, but several times. You must expose the film to light, then stop before it is over or under exposed (which can change the tint and color and saturation of color film even on modern film stock). You then had to develop the film so that the areas which were hit by photons of light reacted. This involved hitting it with a chemical that made the pigments change, and at the appropriate time to stop it by rinsing that chemical away.
Improper stop baths and rinses could leave the active chemicals on the film and it could continue developing over long periods of time. This can explain some improperly-processed photos and film stock from the WW2 area where pixels "bleed" out of their original areas.
Then take those same subjective properties and time-based temperments and apply them to projecting light through the negative and onto the paper stock -- which is also light sensitive. The amount of light exposure through the film and onto the paper can change the tint, color, saturation, and contrast. Then again you must develop the paper (like film) and stop the development at the proper time -- or else it will continue to develop. Most times you see bleed-out on photograph details it's this stage (the printing) that wasn't stopped properly.
Back in WW2 they were still experimenting with chemicals to get the best most reliable development process. It was a wonderful breakthrough, but it was still in its infancy and it was not perfect. Photos could look a lot like the "real world source" or they could look nothing like it at all. Look at what simple post-processing can do to photos now -- can make them dull or bland and can make them look amazing and vibrant (even if the "real world source" was in fact dull and bland).
It is a very subjective art. There is a lot of interpretation that goes into even color photos. Like you said, what exact color is happening here? Is it like USAAF olive drab, which could weather darker or lighter depending on the environment? Or was it poor photo quality and limited reference materials available for comparison?
Even with ample photographic proof it took quite a bit of sleuthing to confirm some of the colors on my Bf109F 10/JG 2 skin.
So basically what I'm saying is you can get a general idea of things from a color ww2-era photo, but don't try to nit-pick every detail. Take it as a ballpark. If it looks blue? Well... maybe it is. Maybe it's just the 60+ years and poorly cared for and aging photos which aren't very representative. Take it all with a grain of salt and use other references (i.e. texts, spelling out paint chips, etc) to back up your decisions whenever possible.
