Melt the sweetened condensed milk, unsalted butter, and white chocolate chips in a medium saucepan over low heat, stirring consistently for about 5-7 minutes until smooth.

Remove from heat and stir in apple flavoring and green gel food coloring until achieving a vibrant hue.

Line an 8-inch square pan with parchment and pour the fudge mixture, spreading it evenly and tapping out air bubbles.

For the swirl, melt dark chocolate with a teaspoon of butter, mix with red gel food coloring, and create drops on the fudge surface; swirl with a skewer.

Chill in the refrigerator for at least 3-4 hours or overnight until set.

Slice into squares using a sharp knife and serve.