Dath'remar Sunstrider and his followers developed strong physical differences from the night elves way before they created the Sunwell.
"Gradually the exiled Highborne developed striking differences from the night elves. Cut off from the new Well of Eternity, they diminished in height, and their skin lost its characteristic violet hue. In addition, the elves lost their resistance to injury and illness, and they became mortal. Many of the elves died from exposure or starvation during their long journey. In addition to these hardships, the elves were forced to flee the site of their first settlement, Tirisfal Glades, due to a mysterious evil influence that drove many of their number mad." - Warcraft Encyclopedia
They were desperate to succeed quickly. After being exiled from the Well of Eternity, the Highborne began to feel the effects of aging and disease. Their skin had even lost its violet hue, and they had begun to shrink in stature. The Highborne feared that the effects would only worsen over time. - World of Warcraft: Chronicle, Volume I
The Nightborne elves that were cut from the Nightwell-enchanted food diminished into the state of Nightfallen.
Thoughts?