Generously grease and flour 6 (9-inch cake pans.) I only had 3 pans so I had to bake in two rounds.
In a large bowl cream together sugar and butter.
Mix in eggs until thoroughly incorporated.
Mix in vanilla extract, buttermilk and heavy cream.
Mix in half of the flour, baking powder, and salt.
When mixture is combined, mix in the rest of the flour.
Divide the batter into six bowls (about 1 cup of batter per bowl)
Add food coloring to each bowl to create a vibrant red, orange, yellow, green, blue, and violet. (see note on how to make colors)
Pour each colored batter into the prepared pans and spread out into an even layer. (layers will be thin)
Bake for 10-15 minutes or until center is set. Do not overbake. Keep a close eye on them as some ovens run hotter and these are thin layers.
Remove from oven and let cakes cool in the pan until pans are warm enough to touch.
Run a spatula around the edges of the pans to loosen the cake and then very carefully remove the cakes from the pans.
Place on a cooling rack and cool completely.
Meanwhile make the cream cheese frosting by creaming together cream cheese and butter.
Mix in powdered sugar and vanilla.
Place the violet layer down first and frost. Followed by the blue layer, green layer, yellow layer, orange layer and finally the red layer. (frost between each layer)
Place a thin coat of the icing on the cake to create a crumb coat. This will make the cake even all around and seal any loose crumbs.
Once the crumb coat is set, finish frosting the cake.
Slice & serve!
To create more defined layers of frosting between the colors, place the frosted cake in the fridge to allow the cream cheese frosting to firm up before slicing
Colors: Be sure to add in enough food coloring to the batter to make the colors very vibrant. To make orange, create a vibrant yellow and then add drops of red until you have orange. To make violet make a vibrant red and add drops of blue.