This Year's Girl:
We all have the capacity for good or evil, and yes, any given person is able to perform evil acts as well as good. This does make everything seem a washed-out shade of grey, but there is a way to "get the colour to come out"...you have to look at the things a person does when he/she does evil. If they try to make amends, and try not to do that thing again, then we can firmly put them in the camp of "good". Even an attempt that fails to get the "never doing it again" thing right is a "good" act IMO, since the intent is to do a good thing in response to a bad one. At the other end of the scale, an evil person will feel no remorse, and actively seek to do the same kind of harm again for whatever reason. There is no attempt to repair the damage. Vamps are incapable of remorse...they have no soul to prod them into feeling it, and they can't repair a ripped jugular...
So, yes, grey is everywhere, but if you pull back a bit and look at the big picture, sometimes things get a little clearer...not always, but sometimes!