Paint the walls and ceiling all the same light color.  I would go with an off-white color.  When you have walls & ceiling different colors it makes a small room look even smaller.   Pick one or two colors and coordinate your room.   Add these colors throughout your room; taking care not to overdo it.   A colored lamp shade on your night stand is nice.  Maybe a coordinating area rug by your bed, or duvette or accent pillow on your bed will bring you the pop of color you are looking for. You said you have a couple windows.  Try to stay away from heavy windowcoverings.