[Graham Boak]

Air Britain's Flying Training and Support Units mentions Catalinas Mk.I, II and V, plus Sunderlands II, III and IV. The colour scheme will certainly have been Temperate Sea Scheme on the uppersurfaces (Dark Slate Grey and Extra Dark Sea Grey). Older aircraft (ie coming from service without repainting) will have this coming down the fuselage sides to undersides in Sky: later aircraft will have White undersides and fuselage sides, with a high demarcation.

I'm afraid I don't know if any of these would have been amphibians without considerable digging in references, but these were fairly rare in RAF service so I suspect not.