It is always recommended to have ambient lighting in a room when viewing a plasma, LCD, LED etc. The best place for ambient light is behind the panel itself. This way you don't get reflections or glare off the screen. The reason you want some mild light during viewing is the reduction of eye strain & fatigue.
If your watching a movie & it goes from a dark scene to say a bright outdoor scene there is a sudden increase of light that will cause you to squint & can sometimes be a little uncomfortable. By having a soft light behind the screen you keep a more constant brightness in the room. So those dark scenes won't have your room super dark & when the bright scene hits your eyes aren't so shocked.
I am not a personal fan of all the different colors behind the screen but that is just personal taste & many people love them. I do, however, have a dim white led rope light behind my plasma. Sometimes I don't use it but most of the time it's on.
The only time you want a pitch black room is when your running a projector. In this case the lighting would negatively effect the picture quality.
There have been TVs from manufacturers like Phillips that incorporated lights behind their panels that changed color & intensity mimicking what is being displayed on the tv itself. It's actually pretty cool to see in action & isn't distracting like you'd first think. My sister/bro-in-law have one, it's not bad!! It's not something that caught on for other brands but many people add some type of light behind the panel. You should give it a try!!!