Make the White Cake Mix to the instructions on the Box
Separate the prepared Mix into 7 bowls. The colors of the rainbow can be remembered by ROY G BIV — Red, Orange, Yellow, Green, Blue, Indigo, Violet. Make more of the earlier colors and less of the later colors. I used Gel colors for a brighter pop!
Start with Red and put the colors into a greased Bundt pan one at a time around the circle. If you use piping bags the lines will come out crisper.
Bake per Box instructions.
Once totally cooled, remove the cake from the Bundt pan and cut in half. For each half, place a dollop of icing on each end and stand up onto a plate. Cover the cake in icing as desired.
I put marshmallows around the bottom once, and I put skittles in the middle once. Decorate however you like!