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Colour scheme looks simple but I cant work out what the colour of the P4 was the only colour drawing I have come across looks to be a Cream or pale Buff colour. In photographs it looks painted but there is no indication of colour scheme. A possibilty is it could be Zinc Chromate which can be a pale yellow with a tint of green but more research is needed it could just be grey
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I think you might be right with Sky type S another colour I was thinking of is RLM76 sky blueThat colour drawling looks like Sky to me, although the tonal quality of the photograph suggests a darker shade. I don't think Zinc Chromate would be commonly applied to British aircraft (tends to be an American thing). I'd go with perhaps a grey or pale blue for the colour, unless you can find a positive description somewhere for the actual shade used.
All the above is just speculation, so feel free to ignore as necessary...but good luck with this ambitious project.