I have read a lengthy explanation, but I cannot recall where. Apparently Hurricane I Z4791 and Spitfire IIa P792 were involved in some naval related training, could be carrier deck landings, etc.
I think this picture shall help.
AMO A.513/41: "Aircraft in miscellaneous units.-Aircraft in operational training units, air fighting development units. fighter interception unit, special duty flights, fighter experimental establishment, No. 2 School of Army Co-operation and the Central Gunnery School, are to conform to the normal colour scheme for the aircraft role"
AMO A.664/42: "Aircraft in operational training units, air fighting development units, Fighter Interception Unit, No. 2 School of Army Co-operation, the Central Gunnery School, meteorological flights, heavy glider conversion units and other special units of operational training unit category are to conform to the normal operational colour scheme for the role of the aircraft. Heavy types of operational aircraft used for advance training purposes may also conform to the normal operational scheme for the role of the aircraft."
