Upon entering a room, one of the first human senses we use is sight.
Our eyes sends a signal to the brain that catapults our emotions. There have been many studies done confirming the correlation between color and the human emotions.

A monotoned (one color) room will often be perceived as uninteresting and provoke boredom. Neutral colors, such as white and cream, are consider to be colorless and are often used as foundation builders. This is the reason why most home builders paint all the walls, of a new home, a shade of white. White is a neutral color that evokes no human emotion; it causes the eye to continue moving onto other objects of more interest and color.

The most cost effective way to quickly transform a room is through the addition of color on your walls; but be warned..... selecting the wrong colors can also have a negative impact on a room's vibe or harmony.
There is an art to selecting the right combination of colors for a room, which includes understanding the design & architectural style of the home as well as the homeowner's personality and usage for that room.
Selecting paint color for your walls can be intimidating, but it does not have to be. Take the time to look through magazine picture and compile a file of pictures that you like. Then sit in the room, that you're planning to paint, and review the magazine pictures you've selected to help you envision how those colors will look and feel in your room. Once you have reached a decision, take your selected magazine page into your local paint store and have an associate help you find a color to match your magazine picture.
If you become weary with the process, you may want to consider calling in a professional decorator. The benefit of hiring an interior decorator, for color selections, is their ability to provide you with a snapshot image (rendition) of your room with the new selected colors, making it easier for you to decide on your color selection before spending money on paint or a painting contractor.
If you decide to call in a professional, make sure you verify that they will come to the home to work with you in the space you're looking to paint as well as provide you with a snapshot image or rendition of your room to help you with your color selection.