Good vs. Evil?

In life, there are a lot of opposites. For example, chocolate vs. vanilla, is a popular one. White and black, is another. However, the battle that I feel is the most important is the one that's called Good vs. Evil, perhaps even the most popular debate of the opposites of all time. However, we must ask ourselves what makes someone good and what makes someone evil? Is there a gray area to this debate, and if so, what is it?
Good and evil are very easy to identify in movies thanks to pop culture. The person whose identified as evil tends to be unattractive, wearing red or black, and of course inflicting torture to a person that is identified as being good. The good person happens to be attractive, wearing a happy color, perhaps smaller in stature, and of course tends to be victimized by the so called evil person.
But sometimes, we must realize that good people do bad things and vice versa. Is this the moral gray zone that author Primo Levi talks about in his work The Drowned and the Saved? I'm sure Primo Levi would classify this gray zone in extreme examples such as a concentration camp, where sometimes one must compromise their morals and do things that they normally shouldn't, and wouldn't have to in a normal life, just to survive. Does that make them evil? I think you would argue that they wouldn't classify as being evil if you include the grounds that are involved, like their residence in a concentration camp, when all of what makes them human is gone; the stripping of their hair and personal values, and being tattooed. They were branded like animals, who only thought survival as their top priority. Does that make their actions evil? I think not, but you can argue different.
Then we have the example of good gone bad. In recent pop culture/literature, we have two examples of such. The first being Anakin Skywalker, also known as Darth Vader. Anakin was known as the Chosen One in the prophecy, and perhaps one of the best of the Jedi, which in Star Wars lingo translates into the good guys who will fight to create balance in the force. They are the ones that fight for peace, against the bad people. Anyways, Anakin was one of the good guys, but began to lust for power, perhaps for fear to save his wife, Padme, whom he fear he would lose in child birth, the woman who he loved more then anything. He met with Darth Sideus, who showed him how he can save her, however, it cost Anakin his morals, killing many young Jedi, and betraying the ones that he in fact loved. He ended up losing his wife in the end, something that I think is kind of ironic, because that's what he fought to prevent. We watch in the prequel trilogy Anakin go from the good guy to the bad, defender of whats good to the evil that takes the good away. The next example is Lord Voldemart, also known as Tom Riddle. I'm a little fuzzy on my knowledge of Harry Potter, but Lord Voldemort was the one whose primary goal was to kill every one in his path. He took the lives of hundreds. I can't remember his primary goal of why he did take those lives, all I remember he too, was at first talented and gifted (kind of like Anakin), and then slowly turned to evil.
I firmly believe that the debate between good and evil is not a black and white issue, because sometimes good people do bad things, and bad people can eventual do some good. I guess it's a balancing act, a ying yang thing. I also believe that without evil good cannot exist, and without good evil can not exist. One can not exist without the other, and I guess that I have no firm opinion to the issue. But that's okay.