Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.

In a large bowl, whisk together the flour, sugar, baking soda, salt, and cocoa powder.

In a separate bowl, combine the vegetable oil, buttermilk, eggs, white vinegar, vanilla extract, red food coloring, and blue food coloring. Whisk until well combined.

Pour the wet ingredients into the dry ingredients and mix on low speed until just combined. Be careful not to overmix.

Divide the batter evenly between the prepared cake pans.

Bake for 30-35 minutes, or until a wooden skewer inserted into the center comes out clean.

Let the cakes cool in the pans for 10 minutes before inverting them onto a wire rack to cool completely.

In a large bowl, beat the softened cream cheese and butter until smooth and creamy.

Gradually add the sifted powdered sugar, mixing until well combined. Add vanilla extract and milk (if using) and beat until the frosting is light and fluffy.

Place one cake layer on a serving plate. Spread a generous amount of frosting over the top.

Carefully place the second cake layer on top. Frost the top and sides of the cake.

Decorate as desired. Chill for at least 30 minutes before slicing and serving.