Put the chocolate chips and half of the sweetened condensed milk in a small saucepan. Heat over medium heat, stirring constantly, until melted.
Quickly pour into the prepared pan.
Place the pan in the refrigerator for 15 minutes.
Place the white chocolate chips and the remaining sweetened condensed milk in a small saucepan and add the food coloring. Stir to combine then heat over medium heat, stirring constantly, until melted.
Quickly pour into the prepared pan on top of the milk chocolate.