How did you plan your nursery colors?

Due with my second son in October. My style is neutrals colors - white, shades of brown and a tiny pop of green. I have a white changing table and a brown crib, but I cannot figure out how to tie all the colors together.. I can't decide what furniture should be which color, etc. some of the things I need are:

Curtains

Fabric to cover my rocking chair

Organizing baskets

A rug.

I wish there was a way to test out colors and design the room before buying. Anyone have advice?