The marshmallow mixture is tinted green to make these cereal snacks look like holiday wreaths.
Line 2 baking sheets with nonstick foil or parchment paper. Lightly coat a 1/3-cup measure with nonstick spray.
Stir marshmallows and butter in a large saucepan over low heat until melted and smooth. Remove from heat and tint with 5 or 6 drops of food coloring. Gently stir in cornflakes.
Scoop 1/3 cupfuls of the mixture and drop into 6 piles on each baking sheet. Let cool 5 minutes. Spray fingers with nonstick cooking spray and shape each pile into a wreath, gently compressing the flakes together. Refrigerate until firm.
Decorate wreaths with nonpareils or candy balls, attaching them with a dab of corn syrup.