There is no silver coloring paste.What you are seeing is Lustre dust which is silver that is mixed with small amounts of alcohol like Vodka or lemon extract.You then paint with a small artist's brush the silver paste onto the areas of your cake that you want silver.
Yay for CC and all the great info on it. 
Americolor has a silver sheen color that you put in your air brush or you can paint it on the after it dries you cake dry brush it with silver luster dust it really brings out the silver and shine I used this method on some dog tags on a Army cake they looked like the real deal.
Moly2
i use Lucks silver airbrush spray....i get it at pfiel and holding
http://www.countrykitchensa.com/catalog/product.aspx?T=1&ShopId=38&CatId=596&SubCatId=149&productId=631910
They do make silver/gold/pearl airbrush color though I haven't used them so I can' t comment on how they work. I usually use silver dust (not luster dust, but actual silver or gold or super pearl) diluted with vodka and spray that through the airbrush.
I just used the Amerimist Silver & Gold sheen on a bunch of stars I used on Hollywood theme cupcakes. It worked really well. Just a hint: Color the white fondant a light gray before you use the silver. You won't have to use so much to cover the helmet.
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