Actually color film was around for a good time before the 40's the issue was, is that it was really expensive to produce, and black and white was cheaper. A good example of a colored film from the 40's would be "The wizard of Oz" (1939). Now the army likes to be cheap but effective at the same time, because of this they used black and white film for footage because it was cheap, and effective at the time. As for the question about saving private Ryan, the answer is saving private Ryan is actually recovered recon footage made by the Nazis following the deployment of private Ryan who at the time was a target of interest for them. You see Private Ryan was a test subject for Army project cicada. This was a super soldier project during ww2, in which soldiers were injected with different mixtures of steroid and speed in order to create the ultimate soldier. The Nazis, wanting to start their own similar program, had the SS film footage of how Lrivate Ryan acted on the battlefield. It is colored film because the Nazis preferred to use it to get a better detailed view of the picture for study.
