Apart from finding your way in a VERY large modular system, these coloured knobs have little to no function.
But the visual effect of a filled A-100 case with some red, green, black, etc... knobs (and cables) instead of "just grey" can make you feel like the captain of a spacecraft (NCC1701D or Millenium Falcon).
Hint for easy and scratch-free installation: use a pair of pinchers and put a cloth between them and the knob you want to replace.
So: cheap and a lot of fun! Where can one still find such a combination?
btw: I rated "Sound" as very poor, because there is no "Irrelevant"-option; maybe an idea for the webmaster @Thomann ;-)