The neutral blue livery was indeed because of local co-operation with Air France on the Internal German Service / Berlin routes when the Super 1-11s (as they were grandiosely christened) began to arrive. There was no other local sensitivity around use of branded aircraft on the IGS and indeed Pan Am had no such issue with their 727s flying on the same routes.
As others have mentioned, the -510s (One-Eleven 510EDs to be precise) had bespoke flightdeck layouts - to keep the post fairly simple, the switching on the overhead panel worked in the same way as the Tridents so that the flow of switching was towards the nose was "on" and towards the tail was "off". On the other 1-11s including the -400s and the aircraft inherited through the BCal take-over, the overhead panel switching worked in the opposite direction. This presented a fairly major issue in operating the types simultaneously and so neither BA Flight Ops nor the CAA would accept flying both the -510s and other variants. If I recall correctly, the three 1-11-539GLs (G-BGKE/KF/KG) ordered by BA in the early 80s were the same as the -400s which is why you tended to see those aircraft at Birmingham and not Manchester.
The 510s also did not have forward airstairs which was a monumental pain from a ground handling perspective - this was another BEA "customisation". Urban mythology was that they had a block of concrete under the forward galley as a weight/ballast compensator for the absence of airstairs - not sure if anyone can confirm whether this was actually true!
The performance on the -510s was never as good as the other -500s, but of course, many of the ex-BCAL/BUA aircraft had been ordered with Med charter operations in mind and so had higher MTOW (about half a tonne more) and water injection which I don't recall the -510s having. BA did some longer sectors with the ex-BCAL aircraft particularly from Birmingham into Spain - BHX/BCN was daily (the BA5328 sticks in mind), BHX/AGP and BHX/FAO at weekends which the -510s wouldn't hack.
Apart from the aircraft which were retired to Duxford (still there) and Cosford, the 1-11s were sold as a batch to European Aviation and most saw service with European Aviation Air Charter. One of many things you had to watch was the closing mechanism on the holds - I can remember one turnround looking after a EAAC subcharter down in Jersey where the door came off the runners (easily done) and shouting at the top of my voice to get someone across to help before the bloody thing fell out of the aircraft completely if I let go. We then had a CSDS failure on the same turnround (where that distinctive whining noise of the starter motor just kept getting ever higher-pitched until it eventually failed!) and so the aircraft didn't go anywhere anyway...
Last edited by Flightrider; 8th Jan 2023 at 15:36.