Maybe Verin is Black Ajah.Verin might possibly have lied. First she told egwene that she only used the dream ter'angreal once, I dought that a brown ajah could resist all the knowledge that she knows is in T'A'R. Second in The Great Hunt she tells Rand that Moiraine sent her but later Moraine says that she didn't, now maybe the wording is different but I don't think so. If she is black then she probably has been plotting to try to get Rand to trust her.