"There's a bane somewhere (...), you may have heard it called a light bane, it's a temple to the false gods (...). A bane corrupts light itself, and drafters more strongly than most." Commander Ironfist, The Blinding Knife
The existence of a blue bane lead to random displays of order in strange places. The White reports she saw birds fly in a straight line instead of the V formation they generally use, even to exhaustion and death. Kip witnesses people suddenly walking in synch in the streets. There are other occurrences that have been witnessed through the books and many others certainly happened without any of the point of view characters being aware of them.
The green bane leads to sudden wildness in animal, meteorological and human behavior.
Banes appear to allow Color Wights to more easily channel their power and to transform faster. The existence of a Prism also seems to prevent the appearance of banes.
Banes appear as floating islands of luxin of a specific color. In the middle stand a circle of twelve pillars of luxin with a Wight in each. In the center of circle may be a spire, in which the avatar of one of the Old Gods prepares to wake.