On Thu, 13 Dec 2018 16:57:52 -0000, Steve Walker wrote:

On 13/12/2018 16:42, Fred Johnson wrote:
Can anybody else remember blue traffic lights on railways? Can't find
any evidence on google. I'm sure whereas cars have red/amber/green,
railways always had a 4th blue light. What does it mean and why has it
disappeared from Google?

Never heard of it.

4 (& 5)-aspect signals have always had red, green and two ambers as far
as I know.

I know that the semaphore signals had lenses that were red and blue, but
they definitely showed as red and green when lit from behind by
yellowish oil lamps at night.

It's possible I'm remembering a switched off light. It was 30 years ago. But they were electric lamps - maybe they still used the same lenses? Maybe they had longer lasting yellowish filament bulbs? Road traffic lights at the time were green lenses, with I think a white bulb.