[Graham Boak]

Light grey undersides were not seen in the Middle East (other than on early Fleet Air Arm aircraft in Sky Grey) before the use of the Day Fighter Scheme (Medium Sea Grey) in Italy around 1943-4. It is exceedingly unlikely that any repainting was done during the Greek campaign, using any colour. They were operating at an extreme edge of supply lines, and anyway why should they?

Aircraft were delivered in a mixture of colours and fits, as you say, but I've no knowledge of which individuals had Vokes filters unless they can be seen on photos - it is safe to presume that the few desert-camouflaged ones did and presumably those seen with the light leading edges and mottle.

I think it is safe to suggest no more than that the majority of the aircraft are likely to have had blue undersides, and that's is what I would use. Given the Temperate Land colours, there's a possibility it could have been Sky. I prefer to accept the comment that Hurricanes going overseas had blue: others may differ.