Open the can of condensed milk and pour about 4 oz of milk into a measuring cup.
Color the 4 oz of milk with 12 drops of yellow food coloring and 5 drops of red and mix until you get orange.
Put foil in a 6 x 6 or 8 x 8 square pan to make it easy to dump the fudge out when it is finished. Cover the entire pan with foil, including the sides.
Melt the semisweet chocolate chips in the microwave for 30 seconds at a time, stirring after each 30 second interval until the chips are completely melted.
Stir in the condensed milk that is still in the can (not the orange milk) to the melted chocolate chips.
Cut the butter into small pieces and add about 1 1/2 T. to the melted chips. Microwave for 30-45 seconds until the butter is melted and stir.
Add 1 1/2 t. of vanilla and stir until smooth. Pour the mixture into the prepared pan.
Now, you need to work quickly and repeat the process with the white chocolate chips.
Melt the white chocolate chips for 30 seconds at a time in the microwave, stirring until completely melted.
Stir in the orange condensed milk to the melted white chocolate chips.
Add the remaining 1/2 T. of butter to the melted chips. Microwave for 30-45 seconds until the butter is melted and stir.
Add the remaining 1/2 t. of vanilla and stir until smooth.
Pour the orange mixture onto of the chocolate and mix with the edge of a knife to swirl the colors.