Line an 8" x 8" pan with 2 pieces of parchment that are 2" longer than the pan on all sides, arranging in the shape of a plus sign.

In a medium pot over low heat, cook chips and milk, stirring occasionally, until melted and smooth, about 5 minutes.

Add Marshmallow Fluff, butter, vanilla bean paste, and peppermint extract and cook, stirring occasionally, until heated through and well combined, about 1 minute.

Divide fudge among 4 medium bowls, about 1 cup per bowl. Add about 4 drops black gel food coloring to 1 bowl, and about 2 drops pink, yellow, and teal to remaining 3 bowls?1 color per bowl. Mix to combine, adding more food coloring until desired color is reached.

Drop a few spoonfuls of each colored fudge randomly into prepared pan. Swirl with a toothpick or paring knife so the colors intermingle.

Refrigerate until set, at least 2 hours or up to overnight.

Using parchment overhang, lift out fudge and transfer to a cutting board. Cut into squares.