Once I got to researching it, I learned that's it's really not difficult at all. It's actually quite easy.
Here is how you do it:
To make the cake you need 2 boxes White cake mix. You also need food coloring in 6 different colors. Most people would use the traditional "rainbow" colors, but we didn't have all of those colors so we used what we had. That would be why we ended up with a black layer :)
For the cake; make one box cake mix according to package directions. Separate batter into 3 bowls with roughly 1 cup batter per bowl. Add desired food coloring to each bowl (purple, blue, green)
Pour each bowl of batter into separate cake pans and bake at 350* for about 15 minutes. Make sure to watch it carefully since it is a smaller portion in each pan, it will be done quicker than normal. Remove from oven and allow to cool completely.
Repeat for next 3 colors (red, orange, yellow) You will now have six layers of different colors.
For the frosting. Here is my buttercream frosting recipe that I use for cakes and most of my cupcakes.
1 cup butter flavor crisco
1 tsp vanilla
1 tsp clear butter extract
3 tablespoons milk
4 1/2 cups confectioners sugar
Mix crisco, vanilla, butter extract and milk until creamy. Add confectioners sugar a little at a time until throughly mixed. Continue to add milk to frosting until you reach your desired consistancy. *If at this point frosting has a Crisco taste, add more confectioners sugar*
If you would like to color your frosting, you may do that also. I did mine white so that the frosting wouldn't overtake all the colors of the cake once cut.
I try to level each layer of the cake with a large bread knife. Especially for this cake because it will end up being 6 layers, you don't want it to be crooked when you are done like mine was. :(
Start with the Purple layer first (or in my case blue). Put the first layer on your cake stand or plate. Add enough frosting to cover the layer and some to spill over the edges, anywhere from 1/2 to one cup of frosting. Run the flat, straight side of a knife around the cake to smooth out the edges.
Repeat with each additional layer until you have completed all 6 layers. NOTE: I ended up making 3 batches of frosting - just so you know.
This is what my cake looked like when I finished frosting all 6 layers and after 2 batches of frosting. I made a third batch to put some decorations around the top and bottom.
After adding some decorative touches, I ended up with this.
See how crooked it is? Ughhh... I should listen to my own advice. I was just running out of time and still had to make basketball cookies for Zachary's basketball game.
Victoria was very pleased with how it turned out and her friends all loved it. At least that's what they said!!
Victoria cut the first piece and here is what the inside looked like.
See why I wanted white frosting? Otherwise, the colors of the cake wouldn't have stood out like they do.