Earlier quoted context omitted.
If it's dark you can't see which light is at the top or bottom. You see a lit light, but can't see the unlit lights. The black boards with white borders are a relatively recent addition to traffic lights, and they're not fitted to all UK lights, which is why our green has a bit of blue added.
No. The official position (as quoted by someone who actually asked the Highways Agency) is that the ability to actually tell red from green is not necessary for traffic lights. The sequence of lights and the positions of the lights is adequate. * http://andrewhenley.co.uk/2012/02/colour-blindness-and-red-t... The statutory instrument that governs traffic lights does not actually state anything more specific than "gre…
This is specified in BS EN 12368.
All your government link says is "we don't want to admit there's a problem because then we'd have to pay for it".
Please note that I didn't claim "traffic light manufacturers are forced by UK law to add blue".