I often heard / read about "Cold is the absence of heat," or Einstein's urban legend, "Evil is the absence of God."

If evil is truly the absence of good, then good is not and cannot be a positive, but is in fact a neutral state of things. Good is just what is, and evil would therefore be what is not. Good is just going through life as usual, not some upward push in morality (as opposed to a downward push of evil).

But if good is a positive, then evil is not an absence, but the opposite end of the spectrum. So is good a positive or neutral phenomenon?

Okay, so if we assume that good is positive and bad is negative ... then good exists and bad also exists, can two opposite exist and conceived to be true at the same time or in the same pattern? A physical body is either alive or dead. In the presence of light, there is no darkness ... but light is not neutral though. What I'm saying is that good could exist as a positive aspect without the condition of having an opposed energy called bad / evil.

Yes. This is logically possible. A body is a complex construct. It does not all die at the same time. There is a gradual phase as parts of the body dies while other parts are still living. It is far easier to say that something more simple like consciousness is either existent or non-existent. There is also no such thing as absolute darkness except under special conditions because in most cases there are still a few photons bouncing around here and there even if we don't see them.

Could positive good exists without negative evil? Sure. Under some conditions. But this will be very hard to accomplish given that good is a subjective concept. Not everyone is going to view it as good 100% of the time. Even if they don't view it as evil, they may view it as neutral.

I, for one, don't believe good and evil to be real entities. I think they are just ways in which we describe our feelings about certain behaviors at any give time. And that those feelings are seldom uniform.