Bashiok: The glow on the shields of Skeletal Shieldmen actually serves a couple purposes. First it's an easy and quick way to identify them from other skeletons, that's a given, but the second function is that it's actually a status indicator. Obviously as you hit them they'll block the hits with their shield, but they can only block so much damage. As they block damage the glow dims. It's a useful tool that visually indicates how close their shields are to breaking.