Since learning the resistor / capacitor colour coding  system in early 1960's  I've used it to great advantage in my domestic life as well as ( obviously ) in Electronic aspects , you know the one I mean , ie , Black - 0 , Brown - 1 , Red - 2   and so on .  In the Electronics Industry when " wiring in " or " Looming up "  cables or wires  , one uses the colour coded system  type identifying Sleeves or Markers  , but when you're dealing  cables or wires that are pre-wired / fixed or have connectors already attached , then the use of coloured insulating tape can come into play . But this is where we hit a stumbling block . I've yet to find Orange ( 3 )  and Mauve / Purple (7 )  insulating tape available commercially  , ironically  the colours have been available in Mic cables and such like , but Not in " Insulting " tape ( insulating tape for the non-cynics out there ) . In my own workings what I do is , for 3  ( orange )  I use 1/2 width tapes of red ( 2 )  and  yellow ( 4 )  therefore the happy medium being 3   , and  blue ( 6 )  and grey ( 8 )  giving  a happy medium of  7  . I find this works perfectly because for the normal colours used  one uses the full width of tape  and the " made up colours " in 1/2 width .  

 So Please  " SELLOTAPE"  , " 3M"  and other tape manufacturers out there , give us this day our daily Orange and Mauve / Purple  insulating tapes  , and in anticipation of Mr Clever Dick out there  I've not been able to find them yet even if you have   . !!!  

  The system of colour coding can sometimes outwit ordinary numbers , when say used in potentially "dirty" situations , such  as in a multi-cylinder engine for spark plug recognition , where if a  numeric system was used  grime/grease  could make a dirty 8 look like a 3   or  a dirty 4 look like an upside down 7  and so on . With the colours used for a V8 engine  it  would be Brown -1 , Red - 2 , "Orange" -3 , Yellow - 4 , Green - 5 , Blue - 6 , "Mauve" - 7 and  Grey - 8 , and Bobs your uncle and  no misfiring of engine , I've used this appraoch myself and it's ok  . For Microphones  in a Recording studio  such as that  AKG C414  that would be Yel / Brwn / Yel  , that Shure SM 58  would be Green / Grey  and so on .  All the dark cabled  leads to and from Mixers / Recorders / Outboard Equipment  where only a silver or white marker would do ( you try and find a good one that doe'snt immediately shed its colour when disturbed )  can benefit from the tape system , Of course if you have white cables then you can use coloured Magic markers to do the job , but bear in mind that over time the ink does fade .

 Back in the day when I was working in my first job ( an apprenticeship ) with a company called  "Lustraphone "   ( we pioneered Europes first Radio-Mic systems )  amongst all manner of jobs I was working on  , I sometimes had to work on M.O.D. stuff  , this was all right angles in wiring , neatness personified , daily checks by the man in a black suit , white shirt and dark tie  there was a protocol of colour coding for Valve stuff where only Red was used for high-tension , Black was Chassis/Negative , Green was Valve i/p grids , Blue was Valve Cathodes  , Twisted Green for Valve heaters  and a few other codings which I 've forgotten  . But alas todays modern approach seems to have ignored all the sensibilities of yesteryear  , so in some circumstances any colour could be high-tension , point here is never assume , you know , it makes an ass out of  Blah Blah Blah ,      See you soon .