1Spray 9-inch square pan with baking spray with flour. In medium microwavable bowl, microwave dark chocolate chips uncovered on High in 30-second increments, stirring after each, until melted and smooth. Stir in chocolate frosting. Spread in pan.
2In another microwavable bowl, microwave mint chips uncovered on High in 30-second increments, stirring after each, until melted and smooth. Stir in vanilla frosting. Spread over chocolate layer.
3In small resealable freezer plastic bag, place white chips; seal bag. Microwave on High 30 to 60 seconds until softened. Gently squeeze bag until chips are smooth. Cut off tiny corner of bag; squeeze bag to drizzle melted white chips over mint layer.
4Top with chocolate sprinkles. Cover; refrigerate until firm, about 1 hour. Cut into 4 rows by 4 rows.