The blue humans have a small explanation for why they resemble human females. Whether you choose to except the explanation is left up to the player, because I don't think it was confirmed. They may or may not look different depending on who's looking at them. Example, they resemble humans to us, while they may look more like a Turian to a Turian, etc.
Whatever you choose to believe, Asari are hot. I would totally do one.
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~Halo Everybody run!
http://img9.imageshack.us/img9/6195/furriese.jpg