Add corn syrup to a small saucepan over medium-high heat. When syrup begins to bubble around the edges, continue to cook for 1 minute. Do not overcook.
Divide syrup into 4 small bowls. Stir 2 drops food color into each bowl.
Use a fine bristle artist brush to decorate cookies; if desired, add candies. If "paint" starts to set, reheat in microwave for a few seconds. Dry thoroughly in a single layer before storing in airtight container.