Pick out about 1/2 cup of the marshmallows from the Lucky Charms cereal for topping the bars later, then line a 9×9 inch pan with parchment paper and set aside.
In a large pot over medium-low heat, combine 7 cups of mini marshmallows and butter. Sir continuously until melted and smooth.
Remove from the heat, then stir in the vanilla extract and fold in the Lucky Charms cereal.
Fold in the remaining 1 cup of mini marshmallows, then transfer to your prepared pan.
Lightly press into an even layer, then top with the reserved Lucky Charms marshmallows and let the treats stand at room temperature until set, about 1 hour.
Use the parchment paper to remove the treats from the pan, then use a sharp knife to cut the treats into equal sized squares.
In a microwave safe bowl, combine white chocolate chips and vegetable oil. Microwave in 30 second intervals, stirring in-between, until melted and smooth.
Add green food coloring into the melted white chocolate, adding a few drops until you reach your desired shade of green.
Dip the bottoms of each treat into the green chocolate, then place on a baking sheet lined with parchment paper or a silicone baking mat and let set completely before enjoying!