Disclaimer: the shade white is used as an exemplar of light, and black as an exemplar of dark (absence of light). This has nothing to do with human skin colour - indeed most sub-Saharan African cultures have a similar light=good, darkness=evil equation. In Zulu folklore witches ride around on the backs of hyenas in the hours of darkness.

Looking back at our ancestors as smallish tree-dwelling creatures with relatively poor dentition (compared with a carnivore) and very reliant on the sense of sight (good colour vision, not so good low-light vision) it is of no surprise that the hours of darkness held terror for them. Night is the time of leopards and other tree-friendly hunters, whose senses were far more useful in low light conditions. Also, deprived by darkness of the ability to see well, the ancestral primate was much more likely to fall from the trees if alarmed by the approach of a predator.
This, it seems to me, is at the root of human psychological unease about darkness and why dark/black became associated with evil.

This symbolism was reinforced and codified for Western Thought through the Jewish absorption of elements of Zoroastrian religion from the Persians in the period after the Babylonian captivity. Subsequently these influences entered Christian and arguably Muslim symbolism.
Essentially Zoroastrianism viewed the universe as a battleground between the forces of good=light under Ahura Mazda (Ormuzd) and the forces of evil=darkness under the satanic Angra Mainyu (Ahriman). Indeed fire as a source of light was sacred, and so was the sun as the prime example of Ahura Mazda's power and benificence.