Ok, remember the red sister that was sent to Salidar to offer them Elaida's terms? There was a point where she's thinking about how Galina (the black sister that captured Rand) broke her block and knew what Ajah she would choose. I generally assumed she meant red. And then she notes how Galina took a special interest in any she thought would choose red. I'm really beginning to think that the majority of red ajah are really black.