Bring back the days of painting switchgear and trunking orange. 

Table 51 not that many electricians will ever look at it.

Line conductor of Control, ELV and other circuits.

Arguably green should be in there too - as it's not longer prohibited by 514.4.5 (and commonly found in 6-core alarm cables).

   - Andy.

I think green should also be there … but so should all the possible bi-colour combinations with the exception of green-and-yellow. It would make Table 51 very large though … the following are the recognised colours:

Black
Brown
Red
Orange
Yellow
Green
Blue
Violet
Grey
White
Pink
Turquoise

So there are potentially 12+11+10+9+8+7+6+5+4+3+2+1 = 78 possible wire colours in single colour and bi-colour combinations

with the exception of green-and-yellow.

Even that's a bit awkward for pair-18 of larger multi-pair cables (en.wikipedia.org/.../25-pair_color_code).

   - Andy.

Except that GNYE (and YEGN) tracer colours look very different to 60/40 % bi-colouring.

Trace colouring is a dab every few mm, whereas bi-colouring is part of the extrusion.

gkenyon: 
 

Except that GNYE (and YEGN) tracer colours look very different to 60/40 % bi-colouring.

Trace colouring is a dab every few mm, whereas bi-colouring is part of the extrusion.

Presumably the examples of the 25 pair Telco cable shown as 18 and 43 are only used for E.L.V. telecom cables and not L.V. protective conductors.

(en.wikipedia.org/.../25-pair_color_code).

Z.

Except that GNYE (and YEGN) tracer colours look very different to 60/40 % bi-colouring.
 

Absolutely - I can't see anyone confusing a twisted pair with a protective conductor. Although I would have thought that any wire with two colours on it would fall under the definition ‘bi-colour’. Just to confuse things, some brands of twisted pair do look to have more of a thin longitudinal stripe of secondary colour rather than blobs.

   - Andy.

I'd sort of agree Andy … although GNYE and YEGN major+trace is unlikely to meet the 60%/40% rule.

I think, however, provided it's a standard cable meeting the requirements of BS EN 50174 (as specified by BS 6701), it complies with BS 7671 because in this case BS 7671 is supplemented by another standard according to Regulation 110.1.3 (vi). 

Security systems are notably absent from 110.1.3, as are MATV and similar applications, although there is definitely an installation safety standard for TV distribution systems - that, however, has no specific requirements for conductor identification.

Zoomup: 
 

What does B.S. 7671 say we can use these colours below for?

Then there's the nmemonics for the resistor colour code: Betty brown runs over your garden but violet grey walks. Thats the acceptable version!

Jaymack