Black carpet with a white rug. Or maybe go red. Grey goes good with everything.
I Have A Grey Couch What Color Carpet Should I Get?
Blue carpet would look nice. Blue and grey go well together.
Bright orange is popular at the moment, and goes well with gray. For a more subtle approach I like medium blue through navy with gray. My favorite is cream, but this choice is usually better for a home without children or pets.
Tan ish pattern, or at least buy pillows with color so your carpet can match.
I have grey walls and blue curtains, what color carpet should I get?