The Admiralty Western Approaches scheme evolved from a camouflage scheme applied to HMS Broke in June 1940 at the suggestion of naturalist Peter Scott, who was serving aboard that ship. Broke was painted white with large polygonal patches of light gray, light sea blue and light sea green. Broke achieved some notoriety in a collision where the captain of the other ship claimed to have been unable to see Broke. Escort captains observing Broke experimented with similar schemes including polygons of dark gray or dark blue for increased disruptive contrast, while others tried painting their ships entirely white to emphasize concealment. The Admiralty omitted light gray from Peter Scott's scheme. White with large polygonal patches of light sea blue and light sea green was adopted in mid-1941 for use exclusively on destroyers and smaller ships engaged in anti-submarine operations. This was a very effective scheme under typical North Atlantic weather conditions of fog and overcast. Captain class frigates were delivered painted white with a pattern of sea blue and light grey in an American Western Approaches variant. These were colors used in American camouflage measures; but the pattern was unique to ships produced for the Royal Navy and was replaced by Admiralty schemes and colors during refit.[19] The Home Fleet destroyer scheme was similar to the Western Approaches scheme but used darker shades of blue and gray on the rear third of the ship, to assist in station-keeping. British decks were usually dark gray.
The Admiralty's informal approach changed when a branch of the Naval Research Laboratory was established at Leamington Spa under Commander James Yunge-Bateman to test ship camouflage schemes experimentally. Painted models were floated in a large tank and examined against different backgrounds, using theatre lamps to simulate varying lighting conditions
This web site may help with the colour codes.
https://www.whiteensignmodels.com/page/Camouflage+Schemes+Colours/20/
