Weaving requires no extraneous objects or gestures. However, lack of confidence in the success of your weaves will cause them to fail, and habits are hard to break. The example used here was of throwing fireballs. When weaving fireballs, Aes Sedai use a throwing gesture, presumably instinctively. There is no need for it - the strength or accuracy of your throw does not actually affect the fireball, but that's how they feel it should be done, so that's how they have to do it. If they tries throwing fireballs without a throwing gesture, they wouldn't expect it to work, so it wouldn't.

Another example is how Moiraine used her kesiera to spy on others. The weave doesn't need a stone to work, but it's how Moiraine learned to do it, and therefore she couldn't do it without the stone.

Furthermore, when teaching initiates, Aes Sedai use those gestures and do not explain that they are not necessary (that would make them look fallible, after all) so young Aes Sedai learn to channel the same way the previous Sisters channeled, with gestures, and therefore channel as they learned to do it. This in turn gets passed on to the next generation of initiates, and so on.

Wise Ones, and presumably Age of Legends channelers, break this deficiency in their pupils, so they can channel simply by weaving.



As far as I know, two sisters remain completely unidentified (plus one unknown White) so there might have been Yellows.