What about yellow curtains for a shock of color?

The grey feeling of the room (the paint color and the light) reminded me of a room none other than Julianne Moore decorated in an issue of Domino. She used these yellow drapes which I think would look great in your room. I went searching for a photo and found it right here on this site.

See the photo of the bedroom, with the blue bedspread:

http://www.apartmenttherapy.com/chicago/blogging/before-after-julianne-mooredecoratordomino-0508-049198