MGM, Capitol & Mercury label designs
Below are all known UK label designs for MGM, Capitol and Mercury catalogue sequences that included classical repertoire between EMI having post-WW2 distribution rights in the UK and the end of 1959 (Capitol had previously been distributed in the UK by Decca and Mercury by Oriole). All sequences are mono, unless stated. All sequences concentrated singly on classical music, unless stated.
The MGM-D popular music sequence included a tiny amount of popular classical repertoire. 10" and 12" labels were of the same design, though it is unclear whether any classical repertoire was issued on 12" during the relevant timeframe.
I am still hunting out an example of a 78 copy of the very tiny amount of Capitol classical repertoire given a joint release as LP and 78 album (i.e. one album, as far as I can tell).
The later rainbow-rim mono and stereo labels were effectively exactly the same apart from the addition of "STEREO" to the latter.
At least the EMI era labels were plum coloured - whilst the Nixa/Pye distributed label was described as "Plum Label", it was really the same colour red as other Nixa/Pye labels of the day.