Microwave bittersweet chocolate and 2 tbsp. cream, stirring every 30 seconds, until smooth, about 2 minutes. Repeat with 1 1/2 cups white chocolate. In a third bowl, repeat with remaining white chocolate and 1 tbsp. cream; stir in food coloring. In another bowl, mix popcorn and white-colored chocolate. In saucepan, whisk marshmallows and butter over medium heat until smooth. Fold into popcorn. Form into 1-inch balls; drizzle with remaining chocolate.