Green on one wall ... beige on the other walls. Could add curtains in yellow, accessories could be both yellow and green. Could also find a blanket with green, yellow, beige. Room doesn't have to be all green and yellow. Beige is a good color check paint colors and bring samples home, stick them on the wall and live with them for awhile. Also check out carpets which could be multi colored with colors you pick. Doesn't have to be wall to wall. Perhaps a carpet in the middle of the floor or where ever you want to put it. What about these fat heads which come in all subject. Just a few things to think about.

You could use accents as the main color such as this pic:

http://cahillhomes.com/wp-content/upload...

I also like the two tone scheme like this:

http://cityouts.com/wp-content/uploads/2...

Example with a green ceiling:

http://www.visionbedding.com/cached_imag...

Hi, personally I would choose white or silver grey to go with your green and yellow. I assume you have chosen the bedding etc which is green and yellow? If you have then I would suggest to use white paint for the walls, but, bring in some more green and yellow 'onto' the walls. ie. some artwork, or a wall decal or something like that.

Silver Grey - perhaps the same or similar to this :)

http://www.benjaminmoore.com/en-us/paint...

Have a look in the picture below to see how grey walls would look with the yellow and green :) And... also on this website :)

http://blogs.babycenter.com/products_and...

http://www.apartmenttherapy.com/calebs-g...

You could perhaps make your own art by purchasing some remnant fabric in the green and yellow - perhaps some patterned and some plain? Then you would need a few blank artists canvases - and cover these with the fabric - cutting enough to cover the canvas and to go around the back and just staple the fabric at the back. Have a look here to see what I mean and imagine them in your own fabric. Group them together on one wall to make a beautiful statement :)

http://itswrittenonthewalls.blogspot.ie/...

Nursery Wall Decals - in case you would perhaps like these to 'jazz up' the white or grey walls and perhaps put them on the wall nearest to the cot - so as he gets a bit older he can see them :)

http://www.amazon.co.uk/Green-Leaves-Bab...

http://www.aliexpress.com/wholesale?Sear...

http://www.aliexpress.com/item/QZ548-Fre...

https://www.google.co.uk/search?q=green+...

You can use either yellow or green curtains/blinds if you have the white or the grey painted walls.

You may also like these wall letters, which I thought you could perhaps use the initials of your son's name?

http://www.pbteen.com/products/pick-your...

Hope the above helps :)