Dragons have a lot more lore in WoW than they did in WC3.
When the Titans had imprisoned the Old Gods and reformed Azeroth, they created the Proto-Dragons in Northrend. Though, this was an experiment, and their second attempt sucessfully made the Dragons. Five Dragons were blessed by each Titan with their own powers to lead the Dragonflights.
Alexstrasza the Lifebinder - Red
Neltharion the Earthwarder (now Deathwing the Destroyer) - Black
Ysera the Dreamer - Green
Nozdormu the Timeless One - Bronze
Malygos the Spellweaver - Blue
Sapphiron, killed in the campaign by Arthas and raised as a Frost Wyrm, was one of Malygos' sons.