I do think that current special casting effect of grey damage shield gems is inconvinient. THe only thing that appears upon casting is a damage shield buff icon, so you actually cant see if you double cast it (with Sleight of Hand skill) or how much of shield power you get (with Palisade skill and some classes' bonuses). So I suggest to show the numbers of the barrier power you get when casting those gems with Grey font colored numbers like this:
(+1681)
(+1681)
So you can see your double casts with grey gems and the shield power, it will help you to know how much aproximately of damage absobtion power you have to plan your actions.