I would do a sharp orange & a very vivid purple. Do you know anyone who can make a quilt for his bed? Maybe a large square of bright orange in the center with a dark purple line/grid around the whole thing? Or maybe skip the bedding & go for the walls. For instance paint the wall his bed is on orange & do a mural or paint a chair rail deep purple then go with khaki or another neutral on the bed.

If he'll let you, try and make the "orange" more gold. There are a lot of purple/yellow sports teams (like LSU, the MN Vikings, the Lakers). Not sure if you're a fan of them or not, but it can lend itself to a sports theme maybe.

Your son is awesome! I would mix solid orange and purple bedding and paint the walls orange and purple with an interesting pattern... Maybe get some cool wall decals from Blik in a pattern/color your son likes: http://www.whatisblik.com/shop/explore

Also, this is a pretty cool comforter in orange: http://www.target.com/Home-Brites-Striped-Alternative-Comforter/dp/B0023E6ESS/ref=br_1_26?ie=UTF8&id=Home%20Brites%20Striped%20Alternative%20Comforter&node=14125291&searchSize=30&searchView=grid5&searchPage=1&sr=1-26&qid=1280771717&rh=&searchBinNameList=subjectbin%2Cprice%2Ctarget_com_primary_color-bin%2Ctarget_com_size-bin%2Ctarget_com_brand-bin&searchRank=pmrank&frombrowse=1

http://lilmagoolie.com/interiors/

the above link gives you options of viewing rooms by the colors. i love the orange and purple combo. i would do a bright orange ( like a sunkist can orange or jelly bean orange) and a deep purple like eggplant or plum. one of the orange rooms had neutral bedding and the walls, accent colors were brought in.

http://www.urbanoutfitters.com/urban/catalog/productdetail.jsp?itemdescription=true&itemCount=80&startValue=1&selectedProductColor=&sortby=&id=18487009&parentid=A_DEC_BEDDING&sortProperties=+subCategoryPosition,+product.marketingPriority&navCount=189&navAction=poppushpush&color=&pushId=A_DEC_BEDDING&popId=A_DECORATE&prepushId=&selectedProductSize=

Land of Nod has a cute set of bedding called "Robo" that might do the trick. The robots don't look like they have a lot of purple in them, but there are grays and blues that echo lavender. It's pictured here with an orange quilt that's really adorable. Maybe show him the bedding and say, "Do you like this? Do you want your room to be in these colors?" He might abandon the literal purple part.

Oops, here's a link to the "Robo" bedding:
http://www.landofnod.com/family.aspx?c=7&f=4898

What a fun challenge!

I think those sheets from Garnet Hill are a great option. I also found these at The Company Store, which I think could work in either the purple or orange:

http://www.thecompanystore.com/LoftHome-by-The-Company-Store™---Rice-Paper/E4C3-ps,default,pd.html?start=1&cgid=sheets-pattern.

I think it's helpful not to look at children's stores, because they categorize things in such rigid girl/boy ways that it's hard to find anything fun that's not navy/red (boy) or pink/lavender (girl).

There is also a set of sheets called "Chandelier" in purple by DwellStudio for Target, which I don't think is girlie at all.

The Company Store has comforters in a dark plum and an orange that could work with patterned sheets.

Then you could accessorize with some items that have orange and purple in them like:

http://www.cb2.com/family.aspx?c=595&f=6071

http://www.designpublic.com/shop/fatboy/5542

http://www.designpublic.com/shop/fauna/9027

You could work in some gray as a break from the saturated colors - a pale gray leaning towards lavender would be nice for the walls, and could have one saturated orange or deep purple/plum wall, maybe. Perhaps a fun little orange shag rug. Some pops of yellow and it'd be a great retro/modern space with an unexpected color scheme.

I kind of picture something with kind of an Ugly Dolls focus - more single color pieces for bedding and the like, and adding in lime green, blue, red, yellow and even black to balance things out. It would be fun to see the result!

Orange is a gender neutral color. I think by concentrating your color scheme on that and adding a dark Purple as a accent will keep it from looking to girly. Stay away from Lilac and light purple and go for a moody eggplant.

When I was in junior high my mom turned my room from girly froufrou pink into punk rock lime green and dark purple. Even now (nearly a decade later) the room at my parents' house is the same paint scheme (but filled with parent stuff)! My suggestion is this: paint his room something bright, crazy bright orange, and do his bedding dark purple. I recommend black for the furniture-- mine was a handmedown dresser I was allowed to paint, that could be a fun project for the two of you! The biggest advice I could give is to let him make it his own space (I realize he's only 4 so there's only so much deciding he can do), but as his own space, he's sure to like it a lot longer.

Great bedding suggested above. I also like the idea of adding in a little lime green. The green/orange/purple combo has a very "comic book superhero" feel to me -- very boyish.

If you're still looking for orange & purple room ideas for a boy, here's an idea:

http://www.decorpad.com/photo.htm?photoId=82613&index=4&searchQuery=boy's rooms&searchType=photos&spaceId=4

I love how they used the colors, and the orange & purple look great together!