i would think about something from West Elm. They have several that I think would look nice in your room; Carved Circles, Clover etc...
http://www.westelm.com/shop/bedding-bath/duvet-covers-quilts/?page=viewall

Pick a tone from the textiles or the pillows - they already go with the green. A burnt orange or a funky pink would really provide a pop of colour there.

I'm with JulieWpg - my first thought was the mustard/orange color in the wall hanging. The deep teal would be more subtle.

I think lavendar would look lovely... however I understand why someone wouldn't like the purple/green combination.

A plain deep red/maroon would be a good backdrop to the existing patterns.

my bedroom walls are the same color and I have a rich chocolate brown duvet cover and I love it.

Pepper
www.pepperbeaumont.com

I'd go with JulieWpg and abigailb's suggestion of a common solid color from your textiles, or with Lisa Hunter's idea of a textile cover to carry on the theme. It depends on if you want more pattern, or to play up what's already there.

The Company Store has some nice duvet covers - I think the Rice Paper cover in either the burnt orange or teal would look great against that green.

http://www.thecompanystore.com/LoftHome-by-The-Company-Store%E2%84%A2---Rice-Paper-Comforter-Cover-/-Duvet-Cover/DS64,default,pd.html?dwvar_DS64_color=TAN&start=36&cgid=quilts-comforter-duvet-covers

I have a similar color on my bedroom walls (Benjamin Moore Sherwood Green) and I have a white quilt. I have prints with purple above my bed and I find purple tones compliment the color well. Also, I have two large teal square pillows from West Elm and they look great on the bed with the green color. I think this Suzani bedding from Williams Sonoma Home is beautiful and would look great with your green and the textile above your bed. Unfortunately, the prices are steep:
http://www.wshome.com/products/p9237/index.cfm?pkey=cbedding%2Dsets&cm%5Fsrc=hero

I prefer the cream/off white with maybe a wine colored throw at the foot of the bed. Because the walls, headboard, and wood trim are fairly dark, a dark colored duvet could make the room look dark and dingy. Also, you might want to replace your night stands--their style and color clash with the British Colonial look in the bedroom (I may be wrong, but this is the impression I'm getting from the photo).

http://www.cb2.com/family.aspx?c=422&f=5828

I think this color would look great and make the room seem very warm, but I'm not sure if you want to go so "solid". A print in the same color family would be lovely. As the first poster said, there are some good options at west elm...

Our bedroom is a similar color, and we have different covers (both in terms of color and in terms of fabric--we're in WI so flannel in the cold months is a must)for the different seasons--white in the summer, burnt oranges and golden colors in autumn, and dark colors in the winter. All of our covers are solids--I vary the mood with pillow cases to allow for more flexibility.

Since you've already got the great textiles, use them as your guide and pick something from them--you've had lots of great suggestions above.

Here are a couple to check out from Overstock.

http://www.overstock.com/Home-Garden/City-Scene-Damask-Key-Lime-3-piece-Mini-Duvet-Set/4998986/product.html

or

http://www.overstock.com/Home-Garden/Michael-Kors-Phuket-3-piece-Full-Queen-size-Duvet-Cover-Set/5173921/product.html

If you can find a teal and white pattern duvet that would look great too.

I don't love everything at PB, but I do think they have lovely duvet covers....

http://www.potterybarn.com/products/alissa-embroidered-duvet-cover-sham/?pkey=cpatterned-duvet-covers-shams

EVERYTHING goes with green. Even though people don't normally think so, green is actually a very neutral colour. I had a bedroom painted in a bright yellowy green before (I think it was Benjamin Moore "Bermuda Grass"), and I used so many different accent colours that complemented the walls very well. Everything from orange and red to chocolate brown. As long as you find something in the same 'tone' as the green on your wall, you'll be all set.

http://www.westelm.com/products/winter-berry-duvet-cover-and-shams-b541/?pkey=cduvet-covers-quilts

http://www.westelm.com/products/organic-carved-circles-duvet-cover-and-shams-b534/?pkey=cduvet-covers-quilts

Just go with even more Indian textiles on your duvet cover.

I'm digging plain white.

What about this duvet with Marimekko fabric - beige and white?

http://www.crateandbarrel.com/outlet/bedding/marimekko-sarafan-almond-bed-linens/f35978

I have a similar pattern in my bedroom (but a bit simpler) and love it.

Restoration Hardware:

http://www.restorationhardware.com/rh/catalog/product/product.jsp?productId=prod100281&navAction=push&navCount=3

I think that this linen duvet in "dune" would look gorgeous. I love the earthy texture and natural linen color.

This is my bedroom. Thank you all for your wonderful suggestions! I'm already torn between all the ideas suggested. The bedroom was painted just before we moved in by the landlord, so I wanted to make it work. And I was quite pleased the textiles I had already went well with the green. Once I make a decision, I'll let you know!

dcirene - I totally agree about the bedside tables. We just were trying to make due with what we had since we moved (and until recently I was out of work).

I used this one with a Moroccan inspired embroidery pattern in a room with a pear green colored wall. I think it looks great without being overpowering. Feels like much better quality than the $24.99 price tag would suggest.

http://www.bedbathandbeyond.com/product.asp?SKU=122382&RN=27&

I would do something simple and classic in here for the duvet cover, and bring in some color with the accent pillows, and a throw blanket at the end of the bed.

http://www.bellahomefashions.com/hotel-style-palermo-estate-white-brown-duvet-cover-set-p4029.html

linen

Why not go with an indian bedspread? The wonderful thing about those textiles is that they work so well together. If you're going with the "marakesh look," then layering all kinds of patterns and color is the way to go!

Whatever color you would call the color of Grey Poupon mustard. Yellow-gray-green-cream. I'm drawn especially to the mustard color in the textile above your headboard, but that might be too much for the bed (maybe not). The poster above me suggested linen and I like that, too. I'm thinking just a touch more hue than is in linen. Btw I like very much your wall color, and room in general.

I'd go with a crisp white duvet with shams and decorative pillows in fun, bold colors that go with the green.

I think your bedroom needs texture more than it needs added color or pattern -- you've got plenty of the latter. I'd keep it white or cream, and find something with some a lot of texture. How about this:

http://www.westelm.com/products/organic-matelasse-duvet-cover-and-shams-b435/?pkey=cduvet-covers-quilts

Fog Linen Work has various lovely neutrals.
Am a bit obsessed with them at the moment...

Saffron Marigold has duvet covers with Indian/Moroccan prints, the have a burnt orange/red print that seems to match. It's actually the same one my gf bought a little while back.
http://www.saffronmarigold.com/catalog/product_info.php?cPath=21_35&products_id=141</a href>

I love the plain white...

I'd suggest VISUAL texture, if not physical texture.

Oops, I was interrupted and hit the submit key by accident.

I'd suggest VISUAL texture if not physical texture in one color, but various shades. So a rustic red that is really composed of multi-colored threads of different shades of red, for example. You could go with another ethnic pattern, but I think a rich "plain" color would set the things you have off better.

Believe it or not Wal Mart has an Indian colored thin quilt that is really beautiful, I think would look good with your room. It has all the colors in your room in a really thin stripe pattern. Duvet's are kind of a pain. Plus, you really don't have to spend a lot. It really is a good product.

A muted pumpkin color. Perfect for the cooler weather. :)

Either a solid or an Indian bedspread would work, or you could pile on the eclecticism with an old fashioned pieced quilt (tons of good ones on Etsy), but I agree with arroyo and SherryBinNH that some texture is needed. In addition to their ideas, how about a small print in colors that complement the Indian textiles? Then your special pieces will still stand out.

this simple paisley from Land's End might work, and the no-iron idea is tempting: no iron paisley sheets

Another idea - you could have a plain duvet and put (a) folded blanket(s) on the foot of the bed. We do this because our cats sit there, but it does add color and texture. The blankets can be changed out for variety. You could even use a light rug or just a swath of fabric. You can buy fleece and just cut it in the shape you want, no hemming needed.

More Indian Textiles.

With that olive green walls and the decor in general, what is going to work wonders, are the earthy pinks, faded pink. Paint a sheet of paper in different shades of pink and it near the wall, so you'll see what the right shade of pink, but definitely bet on the color pink, is the most ideal.

If you're looking for organic bedding the best in the business is Coyuchi (they also make some of the simplest designs which looks like it would go with your decor). There are lots of places that you can find Coyuchi online and I think there are even a few traditional retailers that carry them. I bought our organic duvet cover at www.edenhome.com because they had the same price as everyone else but the cheapest shipping.