Thanks for the responses so far!
The watch came from a local auction - not a from eBay or an internet auction house. I did check to see any history of a yellow face on eBay but nothing came up.
I’ve seen a magazine advert from circa 1970 with blue and yellow faces - could this been one of those? I can’t imagine yellow would have been popular at the time.
I also don’t have a way of opening the back so can’t see the specific serial number.
We do get quite a few odd watches around here - The Rolex repair centre used to be here (se London / Kent border).
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