The crannogmen say a person has the greensight if they dream prophetic dreams which always come true (moss-green eyes may come with it) (II: 320)
A person with the greensight sometimes dreams as other people, but the green dreams are different (II: 320)
A green dream takes the form of metaphor; for instance, a winged creature bound with grey stone chains to the earth might represent a person who has that creature as an emblem who is chained by preconceptions from achieving his full potential (II: 320)
A person with the greensight can sense when a person is a warg (II: 320)
A person with the greensight might dream of his own death (II: 322)
Some of the children of the forest reputedly had the greensight. Their wise men were called greenseers (II: 323)
Maesters believe that the greensight was not magic, simply another kind of knowledge. They believe that their wisdom had something to do with the faces in the trees (II: 323)
The First Men believed that the greenseers of the children of the forest could see through the eyes of the carved weirwoods, which is why they cut down the trees when they warred upon them (II: 323)
Supposedly, the greenseers had power over the beasts of the wood, the birds in the trees, and even fish (II: 323)
The maesters say that no living man has the greensight (II: 325)
Having the greensight is not enough to be a greenseer. The greenseers were wargs as well, and could see through the eyes of the weirwoods and see the truth that lies beneath the world (III: 107)