Frankly, the modelers' search for definitive colors is like a unicorn hunt. In the mid-1980's I asked the father of a friend of mine who made US federal specification paints how close he was able to come to the government swatches with his batches. He laughed. He then retailed the usual story: all depended on weather, humidity, the current store of ingredients, who was doing the preparation that day, etc, etc, etc. In sum, the final product resembled the government swatch, but he never was able to produce an exact match, and nobody ever expected to get an exact match from his company. I saw the CVN TRUMAN and her escorts at Norfolk VA in March 2011. These were in-service warships in port to resupply, not grungy reserve ships, not immaculate museum ships. The big carrier, a gigantic "canvas" for illustrating the pitfalls of assuming warships could be as ideal as a tiny model, looked like she had an advanced case of paint blight. Her flanks were a patchwork of varying mixes, such a variety of values and subtle variations in chroma you could not really assess which were the "on spec" color and which were renegades. The same went for her escorts, but the effect was not quite as pronounced because they did not have such colossal verticals.
The chances of getting on spec colors 100 years later are remote. There are clues, like the chunk of the side of the BARHAM preserved at the Imperial War Museum which was perforated by a German shell at Jutland, or a fragment of one of HAMPSHIRE's boats washed ashore after her sinking. My favored means to get an idea of the colors is to look at as many period watercolors and oil paintings as possible in museums (less satisfactory, online or in books)---and cross my fingers. An artist has the best possible eye for color. I hit the jackpot when I was reading a book by a person who was around the Rosyth ships in 1914-16. He described their color as "French gray", a keen sense for interior decoration to the rescue. To me this was worth stacks of specifications for long gone ingrediants no doubt randomly assembled by the users.
I find any claim to definitiveness by model paint manufacturers, producers of swatches for modelers, or idealists who think they can hit the bullseye by trying to replicate exact ingredients and proportions of paint produced under quite different conditions 100 years ago to be questionable.
P.S.
I stared at the planks of the HAMPSHIRE boat for about 30 minutes at the IWM in 1993, and my notes taken at the time, not having my MUNSELL BOOK OF COLOR at hand, were "medium gray with a hint of blue". Now, accounting for the immersion of the planks in sea water for who knows how long, and the age of the artifact, 83 years, I present this, again, with crossed fingers. Unfortunately, the BARHAM plate was reversed so that all I could see was the white interior color, but I would love to see the outboard side.
I forgot to mention the best source for approximating WWI RN ship finishes: the extraordinary collections of builders' models of warships in museums from Scotland to England. The colossal HMS QUEEN MARY in the National Maritime Museum should be a natural "go to" for any serious researcher. Museums also have ship models made by maritime artists in this period, certainly an excellent source. The difference between the dark gray of QM and the lighter gray of the massive BARHAM builder's model ought to set off alarm bells. There are reasonably good answers to the color question. Documents and official swatches are indicators, but they are not the Holy Grail.
For example, a careful look at the Charles Pears collection at the Imperial War Museum indicates that Rosyth, where he was during WWI, used a green anti-fouling paint on capital ships and lesser vessels.
http://www.iwm.org.uk/collections/item/object/21401