Abyss
It's lonely in the deep
...We may need to enhance the other dragons again. Look at the Stone paragraph! xD
ALL RIGHT! I vote that Earth dragons get night vision! (See that idea loop there? *Wiggles one eyebrow, since I'm not skilled enough to wiggle the other.*)
You could also give the opposit to fire dragons (they can't be blinded by light) and electroreception (it's sort of like sonar) to water dragons?