Bashiok made a post on the B.net forums with an interesting tidbit of info about the Skeletal Shieldbearer monsters in Diablo III. Unfortunately, the thread he made that post in was very troll-infested, and has since been deleted. Fortunately, some of our forum regulars spotted it and copied out the useful part.
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.
Thanks to Mizentrop and Sein Schatten for the tip and the save.