Line an 8x8 baking dish with parchment paper and lightly grease. Set aside.

Add butter, white chocolate chips, and marshmallows to a large microwave-safe bowl and microwave for 1 minute. Stir contents with a greased spatula then continue microwaving in 30 second increments, stirring in between, until mixture is fully melted and smooth.

Allow mixture to cool for about 1 minute then fold in the colored candies.

Transfer mixture to the prepared baking dish and use spatula to press into a flat and even layer.

Cover with plastic wrap and place in fridge for a minimum of 4 hours or up to overnight.

Lift candy out of the dish using the parchment paper. Remove paper and slice into small bite-sized pieces. Store in an airtight container for best results.