Pale skin is not the special trait of highborne. As I said before Varo'then proves this. Azshara had deep purple skin. Also Illidan who involved himself heavily in arcane art had purple skin. He was not a highborne though. HB was just a social status. Physical appearance varies among them.
Also, NE transformation to HE didn't happen because of arcane. It was because they were cut off from life-giving Well of Eternity. They basically grew weaker.