Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
In a medium bowl, sift together flour, sugar, baking soda, salt, and cocoa powder.
In a large bowl, whisk together vegetable oil, buttermilk, eggs, red and purple food coloring, vinegar, and vanilla until smooth.
Gradually mix in dry ingredients, stirring until the batter is smooth.
Divide the batter evenly between the prepared pans and bake for 25-30 minutes.
Let cakes cool in pans for 10 minutes, then transfer to a wire rack to cool completely.
For the frosting, beat cream cheese, butter, and vanilla until smooth. Gradually add sugar, beating until fluffy.
Frost the cake layers and assemble the cake.