2 months in zone killing drakes and elementals and 70 druid has yet to see a yellow one. They are all white and dark blue. 69 BST cons white and yellow ones. Pretty sure they are all 69-70. Elementals hit faster than drakes however each hit seems to be lower in dmg (very seldom hit for over 600) on me 70 WAR 14khp 2.2kac. Once slowed they seem much easier where slowing the drakes seems to have less effect on overall dmg (no parsing, just tracking heals needed).