In a large bowl, combine the popped popcorn and colorful candies. Use a very large bowl so you can stir without crushing the popcorn.

In a saucepan, melt the butter over low heat, then add marshmallows and stir until melted and smooth. Keep the heat low to prevent burning and stir constantly until glossy.

Remove from heat and mix in vanilla extract. Stir quickly so the vanilla distributes evenly through the marshmallow mixture.

Pour the marshmallow mixture over the popcorn and candies, and quickly stir to combine. Work fast to coat everything before the marshmallow sets.

Press the mixture into a greased cake pan or mold, and let it cool completely before slicing. Press gently for an even surface, then cool at room temperature until firm.