Are you aware that the Germans built a number of railway lines of varying (narrow) gauges when they came for their holidays in 1940? Locomotives I think were French.
Previous to that trams had run between St Peter Port and St Sampson's harbours.
If you take the image into a photo editor and drop the brightness till you have good detail in the sky and clear lettering it suggests (to my eye) that they were originally black but faded somewhat.
As an occasional lurker I have thoroughly enjoyed this thread and hope it continues for many years, cheers! to Alan and all the other amazing modelmakers here.
Not convinced of the greyness of 166, looks to me like it could be white but heavily dodged to prevent blown highlights, the right hand end is suggestive of this to me. Sorry to muddy the waters further.