How do i color white chocolate shells after it settles.?

I made chocolate shells to put on top of cupcakes for a party, I was wondering if i could use some kind of power dust to add color because i have seen it on tv with flowers.If you have any suggestions how to jazz them up .The theme is beach and i'm making chocolate cupcakes with vanilla frosting from scratch.And if you know where i can buy it like at a stop n shop, shaws, market basket where ever let me know in the comment