Night Elves are probably based on Drow or Moon Elves? My guess is the only reason they’re both darker is because of their names and not their species’ developmental connection to their environment.
World of Warcraft isn’t like a bunch of other games or real life. Elves change skin colour like they do clothes and how those elves get their skin colour is based the power source in which they draw from; Sunwell, Nightwell, Moon Well(s), Well of Eternity, etc.
Depending on their source of power, their skin tone changes to reflect it. Sunwell = Light. Nightwell = Arcane (blue?) Moon Well(s) (/World trees) = Dark skin. Well of Eternity = Lighter dark skin(?).
No(ish?) Humans, gnomes and dwarves were once earthern that were effected by the curse of flesh and from it, their rock & metal skin transformed into flesh. Plus, humans can be any colour type. Humans can’t ‘have’ a power source like the night elves, blood elves, and nightborne (used to) have. Humans are just humans.