In medium-size microwave-safe bowl, melt candy at 100% power (high) for about 1 minute total, stopping to stir every 20 seconds, until melted and smooth. Do not overheat pieces.
Stir in corn syrup with a rubber spatula until well-combined; mixture will look grainy. Tightly cover clay with plastic wrap. Let stand at room temperature at least 1 hour to firm. (Let semisweet chocolate clay stand at least 2 hours to firm.)
To roll firm clay, lightly dust a clean work surface with powdered sugar. Knead the clay until smooth. (To soften candy clay that was made several days ahead and has become firm, warm in a microwave for 5 to 10 seconds.)
Tint white candy clay with food coloring, kneading clay thoroughly to distribute color. Divide candy clay in small portions. To form shapes, work candy clay to resemble characters or designs. To roll clay, roll portions between sheets of waxed paper to 1/8-inch or less thickness. Cut shapes with cookie cutters, a small knife, or clean scissors. To keep clay pliable (or shapes from drying) while working with it, place clay and/or shapes on a baking sheet lined with waxed paper. Cover with plastic wrap.
Use this delicious, easy-to-shape white chocolate candy clay as you would fondant.