Line an 8x8-inch baking dish with parchment paper, leaving some overhang for easy removal later.

In a medium saucepan over low heat, combine the white chocolate chips and sweetened condensed milk. Stir continuously until the chocolate is fully melted and the mixture is smooth.

Remove the saucepan from heat and stir in the vanilla extract and salt.

If using food coloring, divide the fudge mixture into two bowls. Add a few drops of pink food coloring to one bowl and blue to the other, mixing until the colors are well incorporated.

Gently fold the cotton candy pieces into each bowl of fudge.

Spoon the pink fudge mixture into the prepared baking dish, spreading it evenly. Then, spoon the blue fudge mixture on top, spreading it gently to avoid mixing the colors.

Use a toothpick or skewer to swirl the two colors together for a marbled effect, if desired.

Refrigerate the fudge for at least 2 hours or until firm.

Once set, lift the fudge out of the dish using the parchment paper overhang and cut into squares.