Hi Graham,
Sparkies work in mysterious ways, that only they know. Normally there are printed sleeves on each end of the cable, but they fade over the years making it a much longer job to trace through. I guess when our Sparkies wired up the K6, they might not have put identifying sleeves on the cables.
What it did mean was that a common cable could used, rather than carrying around a heap of the colour coded cables ( a military thing! ), nothing worse than tracing colours to find someone has used a wrong colour, which can cause confusion.
Richard