Do you like that polka dot pillow with the curtains? Or the stripes on the wall? Could do one of those patterns on a rug. If the curtains will be the only print or pattern in the room, I think you're good with choosing a basic pattern in the rug.

On a side note I love that ceiling.

I'd go with a pattern but make it a really big and simple pattern. Maybe something a little more organic too since all the patterns in this photo are geometric. Try this one:

http://ezinegroup.com/img/Area_Rugs/klaussner-home-furnishings-eights-e5594.jpg

I don't get it. This is a Sarah Richardson room. . .it is done. There is carpet in it. If you are only copying the curtains, and this is not your nursery, then I say nearly anything can go, though solid is a sure bet.

The nursery images are from the first season of Sarah 101 - Sophisto-Nursery

Here's a link to some more images: http://www.hgtv.ca/sarah101/episodes.aspx?sectionid=432&categoryid=7647112885988550283&postid=195493
And the shopping guide: http://www.hgtv.ca/sarah101/guides.aspx?sectionid=433&categoryid=5647357893344851114&postid=195489

Are you planning in doing the wall treatment as well? If not I think you could transfer the stripe idea that Sarah used from the walls to the rug. Striped rugs are easy enough to find if you want to buy one, or there are all sorts of DIY painted rug ideas around the internet.

I'm confused too, your description of your room was identical to this photo. I really wish this site would be better at crediting designs in photos to the original designer. It is like pulling teeth here.

Here are some rug ideas based on the colors you mentioned:

Orange:
http://www.allmodern.com/DwellStudio-Big-Floral-Persimmon-Rug-DWL2789.html
http://www.allmodern.com/Chandra-Rugs-India-Orange-Striped-Rug-IND-1-CUG6416.html
http://www.allmodern.com/Designer-Carpets-Verner-Panton-VP-IX-Carpet-VP-IX-DCA1011.html?piid=2752685

Indigo:
http://www.allmodern.com/Couristan-Super-Indo-Colors-Kasbah-Sapphire-Rug-2150-7600X-CU1269.html
http://www.allmodern.com/Safavieh-Soho-Grey-Rug-SOH515A-FV14303.html
http://www.allmodern.com/Milliken-Modern-Times-Harmony-Indigo-Rug-7980-c651-KC2776.html

Grey:
http://www.allmodern.com/nuLOOM-Textures-Cable-Chunky-Grey-Rug-CB01B-NLO1812.html

if your ceiling is going to be solid you could mimic Sarah's ceiling in your carpet.

I love Sarah's work and this was one of my favorite rooms!

Since the curtain pattern is smaller, I'd go with either a large stripe or a large all-over pattern that isn't too busy, in the same color ways as the curtains.

Examples:
http://www.westelm.com/products/camden-stripe-handwoven-rug-t053/?pkey=cwool-rugs
http://www.cb2.com/roundabout-rug/f6765
http://www.cb2.com/hopscotch-rug/f5803

http://www.landofnod.com/kids-all-rugs/kids-room-decor/blue-orange-bold-stripe-rug/f4900

http://www.landofnod.com/kids-all-rugs/kids-room-decor/blue-crosshatch-rug/f9860

http://www.landofnod.com/kids-all-rugs/kids-room-decor/coast-to-coast-rug/f9709

Either you need to go way bolder than the curtains or way subtler, so as not to clash too much. Solid works too. Take cues from the photos you provided -- any one of those patterns would work fine as a rug.

For what it's worth, I just made curtains out of that exact fabric and am pairing a cowhide rug with it.

how about something from FLOR? We did ours in my sons nursery and love it. That way you can customize your own rug--either do a subtle pattern or a pattern with the colors in your room. WE found it to be much more affordable than an area rug, and i love that I can just pick up a square a wash it off if it gets dirty.

I'd do a large orange and white chevron pattern.

nice call guys, this is totally Sarah Richardson. Here I was, feeling inadequate that mere mortals created such gorgeous nurseries. It makes sense that the photo is of something created by a pro -- I agree that credit is due!

And I kinda like it sans rug. Maybe there could be a small one by the rocker/chair?