Preheat oven to 350 degrees F. Place parchment paper on the cake pan and spread coconut flakes over it.
Bake for 8-10 minutes until lightly golden brown, stirring halfway through baking time. Remove from oven and set aside to cool completely.
In a medium pot over low heat, melt white chocolate bars and milk chocolate. Once melted, add butter and whisk until smooth.
Add sweetened condensed milk, vanilla extract, and salt to the pot and stir until everything is well combined.
Wrap the cake pan with wrap and the aluminum foil. Pour the chocolate mixture over the cooled coconut flakes in the cake pan and spread evenly.
Separate the remaining white chocolate into two bowls. 1 or 2 drops of gel-paste food coloring in each bowl and mix until completely blended.
Pour one colored white chocolate over each side of the cake pan. With a spoon, swirl the colors together in a marble pattern. Refrigerate for at least 2 hours to allow the chocolate to set. Cut into individual pieces and serve.