According to the Stormrage book, the black flight felt that the red flight were weak when Alexstrasza was captured by the Horde during the First War. And I think I read somewhere (maybe the many books scattered in Azeroth) that Deathwing had been her biggest supporter and her being soft-hearted, locked him away deep inside the world when he turned. So lots of hate.
Charge of the Dragonflights
The War of the Ancients (page 13 has Neltharion turning and changing his name to Deathwing)
Ruby Sanctum will be a nice break from ICC, but I'm itching more for Cataclysm.
"They say that the best blaze brightest when circumstances are at their worse."