Your picture is really small so its hard to see. I'm guessing its luster dust.
Hi, i saved the pic to my computer and then got a closer look. It looks like it is sprayed (airbrush(americolor sheen colors) lucks brand in a spray can and also pme brand in spray can. They have the sheen colors that you spray on. It looks like white pearl sheen more than silver, but either color is pretty. hth
I can barely see the cake, but I'd say edible silver leaf. Pricy technique, but gorgeous!! Is that a Faye Cahill cake? Do you have a link to it?