Combine white chocolate chips and sweetened condensed milk in a small saucepan.
Melt over low heat, stirring constantly, until mixture is smooth and completely melted.
Stir in Skittles.
Pour into an 8-inch square pan lined with parchment paper.
Squirt one drop of each color food coloring in a different corner of the pan; use a knife to create swirls of color.
Refrigerate or freeze until firm.