Very nice Xan. I was thinking of doing BERT at first but decided to do the later version as painted by Pavelka, as it is a one-off scheme and will stand out of a collection of camouflaged Nieuports. But in Alan Toelle's article in Windsock we learn that the underside of Hall's Nieuport N 1208 was painted sky blue at the factory. Both Pavelka and Hall have written that the underside was sky blue, and Alan has found information from 14 May 1916 that says to "tint the undersurfaces of the camouflaged airplanes to light blue". He concludes that aircraft with serial # N1201 and higher had the blue undersides. So we can safely say that aircraft with lower serial #'s had the clear doped linen underside, while those later (which would include the early Nieuport 17's) would be light blue.
Also the photo you posted of BERT is the same aircraft, Bert Hall repainted it twice, the second time one side was as shown in the photo, and the other side had the mirror image of his name so it read TREB.
I have one photo of Pavelka's scheme, it appears in the Over the Front issue shown above. I will see if I can find this image online and post it, as I prefer not to scan and post photos from copyrighted books and magazines.
Dave C