The reason for the 'neutral' livery I believe has nothing to do with the status of West Berlin, but because the flights had an Air France code-share (or whatever the equivalent was in those days). I believe that G-AVMS onwards were delivered in the full BEA livery.
The 1-11s eventually operated to LHR but for their first years, MAN-LHR was operated by Tridents or possibly Vanguards.
Ah, so connected with the Berlin corridor operation but more "commercial politics" than international politics. What was the split in the -510 fleet between German internal and Manchester in terms of numbers of units based in each location? There could have been only three delivered in red square livery then, 'VMS, T and U. I am sure I saw a picture somewhere, from my memory of 'MH in the BEA scheme back in the day, but that could well have been a mocked up
PR image.