There is a recipe here on the site which tells you how to add silver or gold ludtre dust to royal icing to get the metallic colors.
Hmmmm well I swore I saw it here....Now I can't find it.If anyone knows where it went please help us find it!!!
Hi, ngerland!! Here is a recipe I found in CC.
Hope this can help. 
Bye!
Sory.
Piping Silver & Gold
Serves/Yields:
Prep. Time:
Cook Time:
Category: Frostings
Difficulty: Easy
Introduction:
Saw a few posts asking how to make gold and silver for piping.....found this recipe and thought I would share it:
Ingredients:
2 ts. Powdered sugar
2 ts. gold silver or metallic dusting powder
clear alcohol
1 ts. piping gel
Directions:
On a small ceramic pale, mix sugar and dusting powder. Add a few drops of clear alcohol (gin or vodka is suggested) and mix with a small palette knife to create a stiff paste.
Add the piping gel, a little at a time, mixing well until the consistency for piing in reached. Use a very small piping bag and tip as needed. The leftovers can be put into a small container and stored in the refrigerator. It will keep indefinitely.
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