But now i'm going to throw you a curve ball Darren - I have found more info on the 21 Squadron scheme. Bit of a throwback to the old pre war fighter command split colour on the undersides, but with sky blue and black, and a fuselage band of sky?
21 Sqdr planes wrecked in Malaya show the black underside port side.
And a photo of one of the 453 Sqdr planes (at the other end of the line up) shows the same black port undersides.
So it looks like the info from the previous post's photo was incorrect. SO hopefully I have not thrown you too far off course.