Nonstick cooking spray
1 16- to 18-ounce box yellow cake mix (plus required ingredients)
1 16-ounce container marshmallow cream
3 sticks unsalted butter, at room temperature
1/2 cup confectioners' sugar
Green and red food coloring
1 12-ounce bag green candy melts
12 red candy melts
1 tablespoon vegetable shortening
3 tablespoons unsweetened shredded coconut