See, what it comes down to, is the early tribal religious beliefs. Ancient man looked to the sky and saw a golden orb, an orb that brought light into the sky and provided warmth. The ancient humans began to worship the orb as a god, after all, the orb was indistinguishable from magic. Maybe it wasn't even that, perhaps they worshipped it out of fear. That fear being, that the orb would go away, and leave behind eternal darkness.
Through fear, we created the concepts of black and white. Anything that was good, we associated with white, or the light, and anything that was bad, we associated with black, or the darkness. In the dark, we were susceptible to nocturnal predators and other unseen dangers.