Hi there Peter :-)
I'll break ranks from the miserable lot!
Assuming the war had carried on that long in the Pacific, I reckon the SR.A/1 would have been camouflaged in Sky undersurfaces, tail and fuselage sides, with Extra Dark Sea Grey topsides. It could have still had Dark Slate Grey / Extra Dark Sea Grey upper surfaces...
Not very exciting but, hey!, there would have been a war on!!
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Of course, the return to bright colours for the roundels wouldn't have happened so early, so nice dull markings! :-)
All the best
Rowan