Common room decoration help?

How about bright primary colors like yellow, red, and blue? Or try a more muted verson of those colors. Also, you can get wall decals that add graphic interest pretty inexpensively - I included a link below to one shaped like a tree but there are lots of designs out there. Google Images "wall decals" will get you lots of ideas. Or you can make your own with black contact paper. Come up with an abstract design and cut it out!