Not many brown or green ones, then.
Were there ever any tangerine ones (NE) before the Tyneside wires came down?
Tyneside was all 3rd rail (apart from the Quayside line). I'm certain there were none in brown, green or tangerine. (The SR DC overhead masts used in some goods yards seem to have had local numbers painted on them.)
I've been interested in these plates for a number of years. For some reason the ScR light blue ones mostly didn't survive all that long, maybe they faded more quickly? Even in the late 80s when I did some Glasgow area line bashing I only remember seeing a few intermittent survivors between Partick and Helensburgh from a forward view on a 303. There were rather more survivors even into the 2000s on the first mile of the line from Glasgow Central but looking at a recent cabride video they all seem to have been replaced.
I don't think there are many ER dark blue survivors, as previously mentioned the Colchester - Clacton line is probably the best place to see them but I think there's still some on the LT&S routes. The line from Liverpool Street to Shenfield had LNER-design cast metal design plates (a few odd ones still survive today) and the extensions to Chelmsford and Southend Victoria had an early BR design of Gill Sans letters and numbers on a dark blue plate (the Woodhead/Wath Line structures had the same or similar design throughout, even on the LMR part of the line).
One other early electrification was the MSJ&A line, at some time the structures were given maroon LMR-style plates with an 'MA' prefix, possibly at the same time as the 25kV electrification into Oxford Road even though the Altrincham line itself wasn't converted until 1971.
As the OP said there do seem to be quite a few LMR maroon survivors, I'm pretty sure there are still some at the London end of the WCML.
