I made red, white, and blue cupcakes for 4th of July this year. It seems just about everyone else in the food blogging world did too :)
I used a white cake mix and added lemon extract to my batter. Separate the batter into three equal parts and use gel coloring to make red and blue. Layer the colors in cupcake foils and bake according to box directions.
The frosting is 1 stick softened butter and 1 package softened cream cheese, powdered sugar and water to the consistency you desire, and vanilla extract.