was it CC2 / 20002?Apologies that this is likely 71, not 74, related... 3-4 years ago now, whilst perusing boat train photos of the 1960s and early 1970s, one image-result was an electric blue liveried class 71 (presume) pre-TOPS era.
My memory cannot recall if the train was Night Ferry, Golden Arrow, or another boat train.
I have yet to find that image again. Does it ring any bells? Do you know which loco was painted thus? It looked stunning.
from https://sremg.org.uk/electric/class70.shtml
From 1949/50 they adopted the initial black and aluminium colour scheme chosen by British Railways for diesel, electric and gas turbine locomotives, however prior to this in 1948/9 N°20002 carried an experimental light blue livery and was exhibited in this colour to the railway executive at Kensington Addison Road station.