How can you achieve a realistic silver color in icing?

what kind of icing is it?
usually colouring your icing grey, then going over with some kind of silver paint work. you can buy it ready made, or air brush colours, or mix some lustre dust with alcohol and paint away.
xx

I'd go with airbrush colors.

I don't have an airbrush. So, I should use gray icing painted with lustre dust and vodka (or clear extract)?

you can buy the airbrush colours and just paint them on aswell, or the lustre dust and alcohol approach.
xx

I tinted the icing gray and then sprayed it with superpearl. Global Sugar Art sells the spray cans and it worked really well. Someone had told me you aren't supposed to use the silver luster dust except on decorations. Apparently it's not that non-toxic.