I'd guess the main problem is how great the problem in green-red differentiating is and how much you need this in your work whether the RN or the Army. For instance the more you have different colour wires to repair the less your chance to get the education and Job. Another example: I wanted to be pilot but I had some 3D problems with my sight and did not get further.
The actor, Paul Newman, was colour blind and was rejected as a RN pilot in WW2. He retrained as a radio operator and gunner instead. Paul Newman Wanted to Be a Pilot but Was Color-Blind — Inside the Actor's Navy Service