Great start on this one, Huberlu - I really enjoyed the Berg as well!
The primer you describe as a grey-blue was, I believe a much brighter colour.
When I visited La Ferte Alais earlier this year I was quite surprised by the brightness of the blue metal primer on the Spad XIII they have there. I was assured that it was authentic. The colour is actually very similar to the colour of the floor in the photo in your last post. If you look at the Sopwith 1 1/2 strutter being built on the Memorial Flight website you'll see a lot of that colour in evidence.
The strut brackets show the colour quite well, although in natural light it is an even brighter blue: