I'm not sure where you've got the sparkling bit from. As to their beauty, that a) Is hardly a new thing with Vampires (I.E. Dracula), and b) That's another long standing fluff convention. There's a reason for it too- The Death of Sanguinus and the Blood Angels suffering from the Black Rage is supposed to be a tragedy, because prior to that they were numbered among the greatest of all the legions, and Sanguinus was second only to Horus (And then only just). So the beauty thing is intended to evoke a "corrupted angel" mystique.