In the late 90's I worked at DERA Aquila. The Military Department of Paint and Packaging was there. There were a series of pictures on one wall showing the various effects of paint when photographed under Infra Red light. One of the sequence showed the results of the then Matt IRR paint and the 'new' eggshell type finish. Although the drab paint was slightly more effective, restrictions on lead based paints coming in at the time and the eggshell finish being easier to decontaminate, being smother, that was the one introduced. The guy who ran the section was once in charge of painting all Londons bridges. He used to make 1/32 and 1/24 commercial model kits of aircraft and vehicles to demonstrate the various paints and finishes. I once asked him the best paint to use on Land Rover chasssi. The answer , which he told was a just quick one, took about half an hour.