Richard wrote:

Fortunately I have a couple of 50m reels of 2.5 T+E dated 2004 ad
goodness knows how much lighting cable.

Go to B&Q and you'll find no evidence that colour harmonisation is
taking place at all, and you'll find all their cable still has the old
colours (don't know if it's date-stamped - haven't yet unwrapped the
reel I bought yesterday!).

David