Two corrections I must make:
1. Myrddraal do have black hair on their heads, just none anywhere else on their body. How anyone can vouch for this I am not certain, as no one has been documented to escape after being raped by one. Their hair has been described as both oily and as having no hint of human luster, which I can't quite understand as oil is shiny. Also, despite many drawings to the contrary, this hair must be long because who would ever give one a haircut?
2. A wound from a Myrddraal's blade does not kill that quickly. A person can survive for days or even weeks; the problem is that the wound will not heal naturally, and it festers as if infected, getting worse day by day.
One comment of my own: I have a theory on how the fear thing works. It is not actually some kind of mystical power; it's just that they hate everyone and everything they see so much that they project it (described in Eye of the World). Humans, being naturally empathic, sense this, and it scares them. But then, who other than the most hardened warrior or at least someone who knows the Myrddraal isn't much of a threat to them, such as an Aes Sedai, wouldn't be afraid of someone who's only concern for you is what fun noises you might make while being tortured?