Let’s set the record straight for the people who insist they fed on demons/siphoned fel magic. Please refer to this post in future when people spout their drivel; its been 12 years and people still get it wrong.
_Even so, the prince’s relatively quick acceptance of dire measures (e.g., draining magic from demons) is by no means characteristic of blood elves in general. The blood elves of Outland have by now discovered Kael’thas’ agreement with Illidan, and they have for the most part become convinced of its necessity.
Most blood elves still live on Azeroth, though. Few of these elves know of Kael’thas’ pact with Illidan, and many would be horrified if they discovered it. Draining magic from small mana-bearing vermin is a far cry from draining magic from demons.
Yet, as their hunger grows, blood elves–particularly those in Outland–are becoming increasingly inured to the things they must do in order to obtain more magic._
- The Warcraft encyclopedia.
If there is only one lesson you deign to remember from your time on Sunstrider Isle, let it be this - control your thirst for magic. It is a thirst unending, <name> - what you absorb must be controlled and released via Arcane Torrent. Failure is to become one of the Wretched… hopelessly addicted and insane.
Seek out a mana wyrm and unleash your Arcane Torrent upon it. Learn to master your power. When you have sufficiently released an Arcane Torrent, return to me.
You’ve done well, <name>. With our arcane sanctums not operating at full capacity, these power cores will go a long way in supplementing our needs.
Though most reports are unfounded, one recent incident demands further investigation. The West Sanctum, one of our primary energy sources, has suffered a terrible malfunction and rumors of Darnassian sabotage are rampant.
Mana wyrms, arcane trinkets, Arcane Sanctums. That’s where they got their magic from. Equating Kael’s Expedition to Silvermoon is like equating Arthas’ Scourge to Lordaeron.
Blood elven eye colour changed largely due to exposure to the Burning crystals which were used for both research and to sustain the gravity defying structures of Silvermoon and Eversong. There’s a quest towards the end of the Eversong experience in which a group of people attempted to purify fel magic for other uses:
Edit: There is also this tweet which is arguably up in the air seeing as the Kael novella will likely never be finished seeing as Micky has his own sci-fi warewolf series and nu-Blizzard don’t much care for fleshing stuff out any more.
https://web.archive.org/web/20170523131958/https://twitter.com/MickyNeilson/status/433059417437650944