We tinted our frostings with Wilton's cornflower blue and violet food coloring pastes (also called icing colors).
Makes about 1 cup
1 (16-oz.) package powdered sugar
Food coloring paste
1. Stir together powdered sugar and 6 Tbsp. water. Tint with desired amount of food coloring paste, stirring until blended.
Note: Purchase food coloring paste at cake-supply and crafts stores or supercenters.