A light shade of green or a warm yellow hue are good choices when looking to brighten up a room. To complete the affect you should accent with bright whites to make the colors pop out. Add some cheerful prints and some nice lamps and you will be good to go.
Anything pale and light will help brighten a dark room. You will have good results from a pastel green or blue, which are both very soothing and opening colors. Avoid glossy finish paints, as they will make the room look smaller.
Dark rooms can make a room appear smaller than they really are. If you are looking to brighten a space think in terms of bright colors. Of course white comes to mind, but there is a wide spectrum of other brightners available: pastels, off-whites, tans and taupes.
Color can't brighten a room. Think about it, if u have a room with little light there's no light for the color to reflect! Also remember that colors u choose look different with all lighting. Try halogen lights to brighten a room, its closest to natural light.