White dragon

The White dragon is a monster speculated to have inhabited Gielinor in or around the time of the Third Age. Evidence is provided that they once existed by the examine options of the Third age ranger armour, which say that it is made out of white dragonhide. Like many other species and races that were influenced by the God Wars, the white dragons were likely forced into hiding or became extinct. It is suggested that the Revenant Dragons inhabiting the Wilderness might be the ghosts of white dragons, since they have two heads, and it is said that many species went extinct during the God Wars. This trait distinguishes Revenant Dragons from other varieties of dragon. However, any connection between revenant and white dragons is only speculation.

 A question asked about the White dragon(s) 

Mod Fetzki: But white dragons don’t exist... ;)

Mod Mark: Potentially. We have all sorts of future plans to do with dragon variants.

During a cutscene during the quest Wanted, a group of Temple Knight Rangers are seen wearing what looks like white dragonhide bodies and chaps