Preheat your oven to 350°F (175°C) and line a muffin tin with cupcake liners.
In a large mixing bowl, cream together the softened butter and sugar until light and fluffy, about 3-5 minutes.
Add eggs one at a time, mixing well after each addition, followed by the vanilla extract.
In a separate bowl, whisk together the flour, baking powder, baking soda, and salt.
Gradually add the dry ingredients to the creamed mixture, alternating with the buttermilk. Mix until just combined.
Divide the batter into two bowls. Tint one bowl with red food coloring and the other with blue food coloring until you achieve your desired shade.
Spoon the colored batters into the cupcake liners, alternating between the red and blue for a swirled effect.
Bake for 18-20 minutes, or until a toothpick inserted in the center comes out clean.
Allow the cupcakes to cool completely on a wire rack before frosting.
Once cooled, pipe buttercream frosting in swirls on top of the cupcakes; decorate with chocolate chips if desired.