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.