For something simple, you could add colored pillows on your grey couch, change the lamp in the corner to a colored lamp shade, and have a colored accent on your coffee table. Are you going to put up artwork also above the fireplace?

I'm not sure that your monochrome scheme will work that well with the browns of your walls and rug.

In an ideal world I think the walls would be white and the rug would be in an single, strong accent colour that would also be used in cushions, decorative objects such as vases and possibly even in some of your art. Colours that I think go very well with black and white are cerise pink, sunflower yellow and lime-rind green. A serious, fire-engine red could also work. Whatever colour you pick, don't have all solid-colour manifestations of it. Some bright yellow chevron cushions, or a red-and-white striped throw will stop things looking too clunky.

I do think you need to get rid of those black-and-white cushions though, you have enough monochrome in things like throw-cushions should be in your accent colour.

I agree about switching the lamp out for a more colorful one. I'd even suggest to add several bold light fixtures, because once you get the grey couch in there, it might look pretty gloomy if you don't have enough light in the place!

I actually think the monochrome scheme works well. The main problems I identify with this room is scale and contrast are lacking. Your lovely white chairs get lost in the white background of your blinds. This room desperately needs drapery to anchor that wall and add some contrasting color (black could even work nicely). I would suggest modern, stationary drapes. Hang something really large to add drama above the fireplace. Here are some examples for drapery:

http://www.home-remodeling-decorating.com/image-files/window,covering,ideas.jpg
http://st.houzz.com/simages/1062381_0_15-5592-contemporary-family-room.jpg
http://st.houzz.com/fimages/83175_1000-w394-h394-b0-p0--contemporary-dining-room.jpg
http://planforhomedesign.com/wp-content/uploads/2012/03/Modern-Curtains3.jpg

Paint the walls something bright, and not tan. Change the rug to something bold, like orange or a big pattern.

Artwork, drapery and pillows to reinforce your monochromatic scheme, or to add hints of color if you prefer.

I agree with a previous poster that if your couch is a cool grey, your cool monochrome furnishings are conflicting with the warm beige walls. If you can paint, choose a more neutral or slightly cool grey.

I'd pick two coordinating, bold accent colors and show it in pillows and artwork.

I think it is going to look really different when the curtains go up. They will fill up that wall. Definitely some art work over the mantel. Maybe a classic Picasso line drawing ? black / white repeat... The main thing for me is that the rug is just too small for that room. I think it needs to be twice the size. Your furniture styles seem to be very classic so you could play around with a rug going traditonal or contmporary. A largetraditional patterned rug with some greys , browns and colors would be pretty. What ever the additional colors are, you can repeat around the room with throws, pillows, art work, etc.

She says she has most of the room "done". This leaves me to think she recently painted, so that's not an option to do it again. I'd pass on the black and white curtains and introduce red into the room for some warmth and colour. The walls already look tan to me so red would work well with red. Drapes in a pattern (not solid colour) with red/white, pillows, artwork, a vase. Simple, easy stuff that can be easily replaced or switched out. Red in the winter, lighten things up and use turquoise in the summer. Easy peasy.

I don't see how a person can have an entire room "done" when they are asking how to add color into a room. Paint the walls again.

Hmm.
Assuming you can't paint the walls, get an appropriately sized rug for the space. You could go for a modern bright multi colored rug. Your art should be bright colors and coordinate with the rug. Frames and mats could be black or white.
Pillows and lamps should be bright as well. Pillows with patterns in colors you like, yes could have a bit of near black or near white in them. Change the lamp shade as others suggested. Red, orange or yellow could work with the wall color. Turquoise or teal would as well. Up to you on choices. The curtains will lend more neutral to the space as with the gray sofa, but it sounds like you are already color accent starved. Pick your accent colors and repeat in shades and patterns in other accents around the room.

I treated this room like an outfit.
khaki pants, black belt, white shirt. need a bright tie now.
Or, Neutral skirt, another neutral top. Bright necklace, shoes, purse, etc.

If all the elements shown in the photo are ones that are staying, I'd say to add some small pops of color here and there, ideally something that can be rotated, perhaps switched out at different times of the year.

In addition to the ideas already mentioned above (pillows, artwork, etc), those could include the following in some bright or bold colors - anything other than the colors you've already got:

--colorful baskets or other storage containers

--vases

--plants, probably really big, leafy floor-size ones

--poufs or a garden stool

--a grouping of 2 or 3 mirrors with colorful frames

--candle holders (could use battery-operated flameless candles)

Another option, given the dark wood floors, etc., would be to include a couple small furniture pieces or decorative items (candleholders, bowls, etc.) that have a mirrored or semi-reflective surface to bounce the light around and break up all the dark colors currently in the room

have fun! Post a follow-up photo after you're done --

Persimmon orange-red. Dabs of it in the form of a lamp, a printed pillow or two. Maybe a large mirror over the fireplace with a strong Chinese-red frame.

How about painting the fireplace a bright color? It could be a fun way of creating a focal point, and it's easier to repaint (than the whole room) if you decide to go with a different look in the future. You'd want to coordinate any artwork above the fireplace to go with it though. You can swap out different accent colors on top of your black & white look and it will be a different mood.

No comment on colour but I agree with the comment about the rug size. It's way too small for the room and makes it stick out like a sore thumb

You say colour, I say color :P

I think you should do away with the black and white curtains and hang your color there. Match it with pillows on the couch.

Not only is the rug too small, it looks kinda ugly in these pics - maybe it looks better in person. In any event, the rug goes with the wall, the white chairs go with anything in there, the black and white pillows - well, they don't go with the brown wall and white and brown rug. I agree with other posters that the grey, brown, white and black neutrals don't all play well together. I'd do neutral in brown/tans, OR black and white, OR different tones of gray. Any of those would be easy to complement with splashes of color - in pillows and then in whatever else you want in color instead of one of your neutrals, be it curtains, a lampshade, a rug, a throw, etc. All together though? Not sure all four of those neutral colors (grey, brown, white and black, five if you consider cream or tan, since it isn't all real whites) will play well together, whether you add color to them or no. Rethink your neutrals, and pick a basic netural background. Not to say you can't add a pop of black (or white or cream), like a lampshade, to a neutral background that doesn't contain that color. But I'd rethink your neutral base and make it more in one of the colorways I mentioned above.

That rug looks like the one i got from costco, its the softest rug in the world. That being said, i also have a very black white and grey color scheme. My couch is grey and i have lucite tables and a black mid century chair. I tried many colors, the one that works best is golden yellow. Dont be afraid to mix gold with all the silver, it will look great, bring in warmth and looks very luxe.

Definitely a bigger rug is what's needed. I'd get a big kilim from ebay like this:

http://www.ebay.com/itm/VERY-FINE-HANDMADE-PERSIAN-KILIM-7X10-AREA-RUG-ORIENTAL-CARPET-HAND-KNOTTED-/140819402955?pt=Rugs&hash=item20c97d90cb

or this:

http://www.ebay.com/itm/VERY-FINE-HANDMADE-TURKISH-KILIM-7X10-AREA-RUG-ORIENTAL-CARPET-HAND-KNOTTED-/140819402925?pt=Rugs&hash=item20c97d90ad

To play devil's advocate, you don't necessarily need to add color. A pop of color adds interest and warmth to a space, but you can also do that through texture, pattern, finishes, and lighting.

This room, for example, is very monochromatic, but still feels warm and complete. Though the tones are all muted, there's still a lot of variety in the colors, so there's depth. And there's variety in the textures, pattern, and finishes: there are shiny hard surfaces, clean upholstery lines, velvety pillows with a rich pattern ... but the only pop of color is from fresh flowers.

I do agree that you need a bigger rug, though. The current furniture doesn't seem to fit the scale of the room.

I LOVE white furniture and I commend you for your gorgeous pieces. I just can't see that room without a beautiful sapphire/aqua/teal on that wall. If you're apprehensive, just try painting an accent wall and not the entire room that color. Bring in gorgeous greenery indoors and you'll have the most beautiful furniture you never knew you already had!

I cannot tell if it's the photography or if the wall color really is sucking the life out of the room. I don't understand how a gray sofa is going to work in that space as is. It seems like it would not work with the current wall color, which appears muddy tan on my screen. Honestly, a different wall color (crisp white or a moody gray) would be the best start. Afterwards it would be a lot easier to ascertain what accent color would work best in the space. Aqua, orange and chartreuse are ones that immediately come to mind.

Barring that, getting all the hues to play with each other in the existing scheme seems like a tall order. The wall color seems pretty jarring.

How did the plant pot sneak in there?

First off, black/white/brown/gray do too work together! There are lots of gorgeous mudcloth pieces and other ethnic art to prove it, and any of them might enhance this room.

I think it's impossible to fully comment on the room until the sofa is in place. I can't parse the rug -- are those black squares and other shapes part of the rug design, or are they things sitting on top of the rug?? (I ope the latter, but they confuse the issue.)

I think I'd look for some ethnic touches (around here, that might be Pier One or Home Goods.) A coarsely woven cylindrical basket might make a base for a table between the Barcelona chairs, for instance. Mudcloth art on the wall. Another basket holding a potted tree with a lot of green in the leaves... Things like that.

The black squares on the rug seem to be the art, waiting to be put on the walls. It seems like it might be mostly photos, which would be a decent way of continuing the low-chroma effect while adding a personal vibe that could dilute the hotel lobby effect.

The curtains will make a huge difference. Definitely needs a bright color - even if just on one wall. the black and white is very dramatic and that should be emphasized with your use of color. Try buying a few poster boards in assorted colors or get some white ones and paint them with samples of colors you are considering using. Hang them on the walls and look at them in different lighting, eliminating the ones you like least over the course of a few days. Go with the color left. I also just recommended a great blog about color to someone else who had a similar question. You might want to also check out the info at Choosing and Using Color in Your Home. Hope you'll post an after picture once you've made your decision and made some changes in the room.

first thing that wall color has to be changed! Gray or white. if you have to have color i would go with a black and yellow rug and curtains in a pattern like your chair cushions.

add a big focal point artwork over the fireplace, with all the colours in the room plus one more (a bright one), so that the eye goes all over the room but lands on the art. make it yourself or have a three-year old make you one. else get one art piece in contrast to room style, like an impressionism or an old-world portrait.

Personally I would prefer either a coloured wall or any shade of grey. That being said, it looks like you may have recently painted the walls and they connect with other rooms as well. Therefore, I think the grey couch could work in this room as long as its not too cool.
I would probably avoid using the black and white cushions as they seem out of place in this room with the tan/white/grey already there. Instead, I would go with cushions and curtains in your accent colour (I would use primary red or teal, which I think would go best with the tan).
On the grey couch I would put cushions in your accent colour and cushions in a tan coloured, natural textured fabric like burlap or linen. I would also reposition the grey couch under the window and move the white chairs to the other side. If you are planning on keeping the rug I would rotate it so that the length of the rug follows the length of the couch. I think the lucite coffee table looks a little small, but I think that could be easily remedied with some interesting centerpieces in your accent colour, maybe an off centered grouping with some quirky pieces like an antique toy.
Lastly, add a large colourful painting or a mirror with an ornate or colourful frame above the fireplace.