Grease a 9x13-inch baking dish with butter or non-stick spray.
In a large saucepan, melt the butter over medium heat.
Add the marshmallows and stir continuously until completely melted and smooth.
Remove from heat and quickly stir in the Rice Krispies cereal until evenly coated.
Transfer the mixture to the prepared baking dish and use a buttered spatula or wax paper to press it evenly into the pan.
Melt the green and white candy melts in separate microwave-safe bowls, heating in 15-30 second intervals and stirring until smooth.
Drizzle the melted candy over the Rice Krispie treats.
Sprinkle with green and white sprinkles for a festive touch.
Allow the treats to cool and set before cutting into squares and serving.