Make the cake mix according to the directions. You can use whatever flavor you want, as long as it's a clear color, like vanilla, for example. You can also make your own cake. I made an orange cake.
After done preparing the mix, separate the same amount into 6 small bowls. Pour in a different color of food coloring into each one of it. Mix it well!
The intensity of the color will depend on the amount of food coloring you pour in.
Preheat your oven according to what it says on the cake mix package. Pour in the red color first, right in the middle of the cake pan. Then pour in the orange right in the middle of the red.
Do the same thing over and over. After orange is yellow, then green, then blue and then purple. Or whatever color you decide do use.
I'm sorry for the pictures. The kids where helping me, so they took it for me! :)
This's how it looks before you put it in the oven
Follow the instructions on the cake mix to bake it. Take it out of the cake pan after is done and apply the chocolate coating.
Chocolate coating: Pour all the ingredients into a pan on the top oven in medium heat and mix it all the time until it's boiling. Pour on the top of the cake. I used mm's to decorate it.