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

In a medium bowl, sift together all-purpose flour, granulated sugar, baking soda, salt, and cocoa powder.

In a large bowl, whisk together vegetable oil, buttermilk, eggs, red food coloring, purple food coloring, vinegar, and vanilla extract until smooth.

Gradually add the dry ingredients to the wet ingredients, mixing gently until just combined.

Divide the batter evenly between the prepared pans and bake for 25-30 minutes.

Cool the cakes in the pans for 10 minutes, then transfer to a wire rack to cool completely.

In a mixing bowl, beat together cream cheese and butter until smooth, then gradually add sifted confectioners' sugar and vanilla extract.

Place one layer on a serving plate and frost the top; add the second layer and frost the top and sides.