Whether you are covered in blood or mud seems to depend on your weapon. When I've used a sword or an axe, faces are covered in blood spatters. When I've used Dror Razglin's hammer, Faithbreaker, it seems to switch to dirt or bruises.
Hmm, that's a track. My monk never seems to get any speck of blood, but she mostly fights unarmed.
But Gale who never does any melee gets blood on the clothes but not on face or hair.
Still I had monks in previous PT's, and I never noticed this effect before. Maybe something did change in patch 7.