I thought about elves and the amount of fel corruption visible in the eyes, so I made a dumb chart. idk if anyone cares buuuuut

1. generic High elf (loser) 

2. I imagine that fel is VERY potent stuff so even a tiny amount  would leave trace amounts, however it would wear off eventually. (I could see players even having a little bit when they run around outland or fighting demons, or making out with a warlock. it would go away in a day)

3. Now this is tricky as the elf would have to be around fel consistently enough to scar, but still so small to barely do anything. Possibly what a child would have (inherited from a parent) or someone that hung around the outskirts of Silvermoon?

4. Someone who never used fel but was surrounded by it. Prolly farstriders or poorer civilians.

5. Average belf who chased an average amount of the green dragon. They would start to show some amounts of sickly baggy eyes, or a tint to the skin.

6. Active fel casters, scars would begin to show and they might even have a darker glow on the whole body.