01 -
Line an 8-inch square pan with two pieces of parchment paper extending 2 inches beyond each edge, arranged in a plus sign shape; optionally secure with binder clips.
02 -
Over low heat, combine white chocolate chips and sweetened condensed milk in a medium saucepan, stirring occasionally until melted and smooth, about 5 minutes.
03 -
Add marshmallow fluff, unsalted butter, vanilla bean paste, and peppermint extract; stir gently and cook until fully combined and heated through, approximately 1 minute.
04 -
Transfer fudge evenly into four medium bowls (approx. 1 cup each). Add 4 drops black gel coloring to one bowl and 2 drops each pink, yellow, and teal gel coloring to the others; mix thoroughly, adjusting coloring quickly to avoid premature setting.
05 -
Spoon colored fudge randomly into prepared pan; create swirls by dragging a toothpick or paring knife through the layers to intertwine colors.
06 -
Refrigerate until fully set, at least 2 hours or preferably overnight.
07 -
Lift fudge from pan using parchment overhang; transfer to a cutting board and cut into squares as desired.