thanks I never thought about brown....
Oh, and the cool thing about using a brown is that when you put his primary colored decorations up, they'll POP off the wall! This is what I plan to do when I have a boy.
My SIL had to have her children share a room (boy and girl). What she did was she painted her daughter's side pale pink and used antique furnishings and on her son's side she painted it chocolate and pale green. The room looked amazing! Especially since brown goes with pink, and it also goes with green.
I think the primary colors will definitely clash with the pastels, so you may want to paint his side a brown and maybe blue or green. And her side you want to paint it a pink or soft yellow. Those colors would go well together!