Work with the rug, keeping the gray of your sofa in mind. Paint your walls blue and add blue and a lighter gray in throw pillows for your couch/

Just showing this mix of darks / but the art has the chartreuse-hot yellow color. Would that be too much in small pattern of rug? or tangerine/persimmon?

Soft Modern Interior · More Info

Mix of FLOR neutrals/ but not over carpet I guess/ nearby?

Pause Studio · More Info

More neutral in grey and coffee, but see there are 3 options. Could use this shape in other places. I've seen Ikea's wide curtain panels like it.

Country & Floral Cosmopolitan 9'x13' Rectangle Pigeon Gray, Coffee Bean Area Rug · More Info

220V Natural Style Table Lamp with Bunched Wood Sticks · More Info

If it's going to get somber a tiny amount of yellow or red or purple or most bright colors would warm it, and I think communicate well with dark brown. To me the important thing is to have a small amount in rug, that you will also have in art [though you don't have to, but another bright then]. Just easier that way, but maybe you'll add shine and gleam!?

Dainostix Fluorescent Floor Lamp with a Modern Yellow Finish · More Info

Rizzy Home Gray 5 x 8 Swing Hand Woven New Zealand Wool Rug · More Info

Modern Lamp Shade - Nordic Winter Collection - Sticks, 18" · More Info

Safavieh Retro RET2140-2473 Light brown, Eggplant 5' x 8' Rug · More Info

Both blue and yellow go well with gray and brown. Tie the two with art, accessories an area rug.

What about a Gray/Tan/Chocolate/Cream combo? See this link for inspiration:

http://www.sweettoothsweetlife.com/2015/04/09/a-grey-and-tan-living-room/

It would even look nice if u added a touch of Aqua or a medium Turquoise (like printed throw pillows or an extra large piece of wall art that has some or all of the colors...Etsy is a great place to find throw pillow covers and wall art prints that have specific color schemes).

Regardless of what room you are decorating, I often find it helpful to look at bedding collections to reference how colors look together. Below is a gray/brown/turquoise/aqua combo:

http://www.oldcalgary.com/cheap-bedding-sets-queen/top-quality-cheap-bedding-sets-queen-fashionable-sweet-gray-floral-patterned-comforter-chic-blue-bedspread-charming-big-thick-brown-shams-stylish-sweet-gray-floral-patterned-pillows-cool-blue-pillows/

Here is a trend board that I had saved a while back that actually has grays and chocolate and a pale green that's a nice color story (I work in the fashion industry).

http://colorpalettes.net/wp-content/uploads/2013/10/cvetovaya-palitra-106.jpg