Whisk powdered sugar, vanilla, corn syrup and water in a medim bowl; should be thick; if too thick add 1/2 tablespoon more of water; if too thin add 2 tablespoons of powder sugar
If you drizzle icing from the whisk and it holds a few seconds before melting back into the icing then it is the right consistency
Add different food coloring; cover and refrigerator when not using; use a squeeze if desired to decorate cookies
Allow 24 hours for the icing to set up and harden once decorating the cookies