Preheat your oven to 350°F (175°C). Grease and flour your cake pans to prevent sticking.
Mix dry ingredients: In a bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.
Cream butter and sugar: In a separate large bowl, cream together the softened butter and sugar using an electric mixer on medium speed until light and fluffy. This should take about 3–4 minutes.
Add eggs and vanilla: Beat in the eggs one at a time, followed by the vanilla extract. Mix until combined.
Add dry ingredients and milk: Gradually add the dry ingredients to the butter mixture, alternating with the milk. Start and end with the dry ingredients. Mix just until combined.
Bake the cake: Pour the batter into your prepared cake pans, smoothing the top with a spatula. Bake in the preheated oven for 25–30 minutes, or until a toothpick inserted into the center comes out clean. Allow the cakes to cool completely on a wire rack before frosting.
Make the frosting: In a medium bowl, beat the softened butter until smooth. Gradually add powdered sugar, one cup at a time, and mix well. Add vanilla extract and milk to reach a smooth, spreadable consistency.
Decorate the cake: Once the cakes have cooled, frost them with the buttercream frosting. Divide the frosting into bowls and add food coloring to create the pixelated blocks. Use a knife or spatula to create the colorful design, or use piping bags for more intricate details.