The CO of 74 Sqn and WW2 'ace', Adolph 'Sailor' Malan flew a 74 Sqn machine in 1940 coded K9953/ZP-A. According to a painting I have seen, he also flew P7370/ZP-A.
The first Spitfires to reach the RAF were painted in a camouflage scheme of brown and dark green. The undersides were painted with one half black, the other white , with the dividing line running from nose to tail, sometimes only the underside of one wing was painted black, leaving the fuselage underside white. K9953 was in this scheme and was the standard scheme for Spitfires in the Battle of Britain up until the Summer of 1940. From then on during the war the undersides were variously light blue, light grey or duck-egg blue. The scheme was intended to either break up the silhouette of the aircraft or provide identification to anti aircraft gunnery units, depending on which history book you read.
There's a bit more of a definitive markings history of 74 Sqn here -
74 Squadron Markings