There are both extant technical reports from the period describing all of the circumstantial variables which would need to be measured and controlled in order to be able to rely upon colour film, which in practical terms couldn't be done.
Furthermore, there are plenty examples of surviving colour film which give an impression which differs from primary source evidence of the paint applied. That does not imply non-control of the paints but only that any resultant photograph is a function of the film behaviours, the development, the average temperature and spectral spread of the ambient lighting, and filters on the camera lenses which were common practise at the time, and of course the component angles between light source, observed planes of the viewed target and the observer with camera.
Given how close 5-D and 5-N really were, I think anyone claimed to have proven this from analysing blue component on old film is way out on a limb. Certainly the analysis I've been party to of Royal Navy subjects has proven to be wildly unreliable. Photos can support analysis and are of course useful. Sometimes a colour which is distinctive can be seen clearly. Trying to pick between two paints of similar tone and have similar pigments of subtly different saturation is shaky ground.