In a mixing bowl, combine powdered sugar and milk.
Add light corn syrup and vanilla extract to the bowl.
Mix ingredients until smooth and free of lumps.
If desired, add food coloring to the icing and mix thoroughly.
Adjust consistency by adding more milk or powdered sugar as needed.
Transfer icing to a piping bag or squeeze bottle for easy application.
Decorate the cooled sugar cookies with the icing.
Allow the icing to dry completely at room temperature for about 24 hours.
For multiple colors, allow the first layer to dry before adding another color.
Store any leftover icing in an airtight container for up to a week.