Complementary colorations - I agree wholeheartedly. It is definitely best to get equipment wiothout colorations and mate them together, the room included. Unfortunately most of us don't have access to the funds, or the equipment or the dedicated room environment to pull this off. We have to make do with what we can afford and/or what we own (expensive equipment alsways seems to have their own voicing too, so that's not a good parameter to go by either).
That's why trial and error in cables is so prevalent. It is easier and less expensive to use DIY cables for these tests, but not everyone is so inclined. Yes, they are tone controls to make up for deficiencies elsewhere. Hopefully the deficiencies are minor enough to correct with a different cable though.
Enjoy,
Bob