Xuu4u, I would recommend that you google gamma correction in general and understand how it applies to the real world and computer 3D graphics applications.  Start with wikipedia.  Once you have a rudimentary understanding, follow up your education by perusing the threads concerning Gc, especially those involving bagginsbill.  It would be pointless to steer you to specific threads which could lead to further confusion and misunderstanding. 

BTW, the reason your scene looks washed out with Gc, too much lighting.