Preheat oven to 350°F.

Spray cooking oil all around 3 pans.

In a large bowl, beat cake mix, water, oil, and eggs and then mix with an electric mixer on low for 30 seconds, then medium for 2 minutes.

Divide the batter into 6 different bowls with about 1 1/3 cups of batter in each bowl.

Use food coloring to make 1 bowl red, one red orange (red and yellow), yellow, green, blue, and purple (red and blue) User as many drops as necessary to get your desired color.

Refrigerate 3 of the colors of batter until ready to bake.

Pour other 3 colors into cake pans and bake for 18-20 minutes and then cool for 10 minutes.

Wash cake pans and put the remaining 3 colors into the pans. Bake for 18-20 minutes and then cool for 10 minutes.

Beat shortening and butter with electric mixer on medium until batter is a light yellow color.

Gradually beat in powdered sugar.

Pour in vanilla.

Add milk one tablespoon at a time until the frosting is smooth. Beat on high speed.

Place the purple layer of cake in the center of a plate.

Put icing on top of the purple layer until fully covered.

Place the blue layer on top of the purple layer.

Put icing in top of the blue layer until fully covered.

Place the green layer on top of the blue layer.

Put icing on the green layer until fully covered.

Place the yellow layer on top of the green layer.

Put icing on top of the yellow layer until fully covered.

Place orange layer on top of the yellow layer.

Put icing on top of the orange layer until fully covered.

Place red layer on top of the orange layer.

Put icing all over the sides of the cake until fully covered.

Put icing on top of the red layer until fully covered.

Final product!