Prepare an 8x8-inch square baking dish lined with parchment paper.

In a large saucepan over low heat, combine sweetened condensed milk, white chocolate chips, and half of the semi-sweet chocolate chips. Stir for 5 minutes until melted and smooth.

Remove from heat and stir in peppermint extract until blended.

Remove half of the fudge mixture to a separate bowl. Add red food coloring to the remaining fudge and stir until pink, then pour into the baking dish.

Pour the reserved white fudge over the pink layer and swirl gently with a knife or toothpick.

Sprinkle crushed peppermint candies over the top and gently press down.

Refrigerate for at least 2 hours until set, then lift out and slice into squares.