One possibility that occurs to me that the dark aura is something that the channeler can control, if he is experienced enough with TP.

Ishy did have such a dark aura, and whats more he actually seemed to control it. For example at the end when Rand kills him he tries to defend himself by pulling on the blackness surrounding him and making it into a "black ball" in his hands.

Perhaps if Rand had continued to channel TP, eventually he too would have gained the ability to manifest/hide and control his black aura at will, but one use was not enough. If true it might be a clue that Taim has touched the TP, but not used it extensively.

Though it occurs to me that this does have the problem that the other forsaken have all touched the TP too. Demandred,Moghedien and others all describe what its like. Why don't they have dark auras? Hmm. Unless they too have used it just enough to learn to control/hide it.



It is likely that the other parts of the halo are a result of Rand being dark!Rand and the effect it has on his ta'veren influence. We see this when all the effects of ta'veren turn bad after the Semirhage incident. Dragon and the land being one and all that.