That's a modified Western Approaches camouflage pattern, and it was symmetrical on both sides. The light colour is Western Approaches White (an off-white, and item RN 10 in our Colourcoats enamels). The darker colour is simply identified as "dark grey" by Alan Raven in his series of books on RN camouflage, However, looking at the contrast between the darker colour and the pendant number, I believe the darker colour could well be B.15 Dark Blue (Colourcoats RN 15), with the pendant number in black. It is possible that the darker colour could also be MS.2 Dark Grey (Colourcoats RN 05). Decks in Western Approaches schemes were generally MS.2. A final possibility is that this is the standard 1943 version of Western Approaches camouflage, using B.55 Medium Blue (Colourcoats RN 17) and Western Approaches White. If that scheme were photographed using a yellow or red filter on the camera lens--not uncommon for aerial photos in that period as a means of reducing haze--on orthochromatic film (as were virtually all aerial films of the period), then the B.55 blue would appear as a dark grey in the final print. How's that for muddying the water?