From the
Glossary of The Wheel of Time:
Societies among the
Aes Sedai, to which all Aes Sedai belong. They are designated by
color;
Blue Ajah,
Red Ajah,
White Ajah,
Green Ajah,
Brown Ajah,
Yellow Ajah,
Gray Ajah. Each follows a specific philosophy for the use of the
One Power and the purpose of Aes Sedai.
The Red Ajah bends all its energies to finding and
gentling men who are attempting to wield the One Power.
The Brown Ajah forsakes
involvement with the world and dedicates itself to seeking
knowledge.
Blues seek causes.
The Green is the Battle Ajah.
Yellows are healers.
Whites follow
logic.
Grays are
negotiators.
There are
rumors (hotly denied, and not safely mentioned in front of any Aes Sedai) of a
Black Ajah, dedicated to serving
the Dark One.