During World War II, some film types made the red darker than the green, some made the green darker than the red. Add to this the time of year and day, the position of the camera and subject relative to the sun, the weather, atmospheric conditions and a bundh of other factors, and it becomes quite clear that it is impossible to determine colour from black and white photographs.
Just look at the Panzers during Fall Weiß and Fall Gelb - it's extremely difficult to see the edges between the Dunkelgrau and Dunkelbraun.