We Have Copper Carpet And We Want A Dark Denim Sectional. What Wall Color Works?

Copper is a warm color, i call it cinnamon...or toast, etc. And so, what effect are you seeking? Re, which room is it in.
yeah, it may matter, somewhat.
bedroom, copper carpet would be the hot or passionate color, but it seems you have living room or den. The color of the floor refects action, friendship, happy words.
the sectional would look good in, believe it or not, a rust tone red. Im not kidding. You could even add a gray throw rug over the carpet, or bluegray.
soft pale or medium gray can go with the mix.
black will show wear easily, sorry! Dark chocolate warm brown will be complimentary color, but oddly, those dont always give the mood you want.
dark teal would go well. But it may be overpowering.
bluegray would be a better bet in a medium or dark tone.
i think a lot depends on your tastes.
personally if you could stand it, white denim would be outstanding but if you go that route, have it scotch garded to make it highly stain resistant.
let me know which way you went and put up a pic here when you can! I am curious now.