Thanks for the colour combo suggestions everyone - keep them coming. I think it needs to be a solid rather than metallic colour in light of the retro fee of the car, but also needs to be "special" and unusual which  pushes white or off white down the list. There also needs to be some Porsche provenance to it but does not have to be a slavishly precise Porsche colour either - that's what would give it a Singer signature. That led me initially down the Heron grey/ Fashion Grey / Slate Grey  (probably too dark) route, but now I'm leaning towards something more pastelly greeny whilst always resisting the temptation to go orange which is hands down my favourite colour .