I want to give gumpaste/fondant shells a pearlized look for a wedding cake. I will be tinting very slightly and want a pretty soft sheen for the shells. What do you suggest I use both for the tinting and the sheen?

When you say "tinting" what exactly do you mean? As far as pearlized effect, you can brush them with a pearl or luster dust. This will give them that sheen you are looking for.