It's pretty straight-forward, Drow scowl in disgust, Elves have an aloof sneer.
As for proportions, Drow should be what Elves would look like if they became underdwellers, so shorter, and perhaps even more wan. With that in mind Drow should be about Human height, but more wiry. And with D&D Elves being already the same height or shorter than Humans, Drow should be shorter than Humans. I think the way I've usually thought about it, humans look life they evolved from primates, while Elves look like they were created to be beautiful, so much so that they become inhumanly beautiful. Like if you asked someone to draw a person but gave them a description of only the most attractive traits, it would look off.
Like someone mentioned, a pallid white is common for creatures that never expect to be viewed in the light, similar to the Drider art from the 3e monster manual(it's pretty rad). That being said, I believe Drow are dark skinned because of their accursed origin, so 'palette swap' isn't exactly a terrible way of describing it.