For the Cake:

1. Preheat the Oven:
   • Preheat oven to 350°F (175°C). Grease and flour six 8-inch round cake pans.
2. Make the Batter:
   • In a large bowl, cream together the butter and sugar until light and fluffy.
   • Beat in the eggs, one at a time, then mix in the vanilla extract and vegetable oil.
   • In another bowl, whisk together the flour, baking powder, baking soda, and salt.
   • Gradually add the dry ingredients to the butter mixture, alternating with the buttermilk, until smooth.
3. Color the Batter:
   • Divide the batter evenly into six bowls.
   • Tint each bowl with a different gel food coloring to create red, orange, yellow, green, blue, and purple batters.
4. Bake the Cakes:
   • Pour each colored batter into the prepared pans, spreading the batter evenly in each pan.
   • Bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
   • Let the cakes cool in the pans for 10 minutes, then transfer them to a wire rack to cool completely.

For the Cream Cheese Frosting:

1. Make the Frosting:
   • In a large bowl, beat together the softened cream cheese and butter until smooth.
   • Gradually add the powdered sugar, beating until light and fluffy.
   • Mix in the vanilla extract and enough heavy cream to achieve a smooth, spreadable consistency.

Assembling the Cake:

1. Level the Cake Layers:
   • If necessary, level each cake layer by slicing off any domed tops with a knife.
2. Frost the Cake:
   • Spread a layer of cream cheese frosting between each cake layer.
   • Once all layers are stacked, frost the outside of the cake.
3. Decorate:
   • Decorate the cake as desired, and enjoy your Luxurious Rainbow Velvet Cake!