I'd forgotten completely that Desert Air Force aircraft had blue undersides.
I wouldn't mind quite so much if I hadn't seen a Spitfire V at Duxford a few years ago temporarily fitted with a tropical filter and in that scheme, and if I hadn't got an unmade plastic kit of one in a cupboard upstairs.
I can't find a picture online after a brief search but this is a video of the one at Duxford.