Preheat the oven to 350 degrees. Line 18 muffin cups with cupcake liners and set pans aside.

Combine all cake ingredients in a large mixing bowl and beat with an electric mixer set to medium speed for 2 minutes. Divide batter evenly between the prepared muffin cups and bake 18 to 24 minutes, until a cake tester inserted into the center of the cakes comes out clean. Cool cupcakes completely before frosting.

Puree the berries in a blender or food processor. Pour into a small saucepan. Add the lemon juice and set the pan over medium heat. Bring to a boil, stirring frequently. Turn heat to low and simmer, stirring often, until puree reduces by about half (8 to 10 minutes). You'll have about 1/3 cup of puree. Remove from heat and cool to room temperature.

Once puree is cool, place the butter in the bowl of a stand mixer fitted with the paddle attachment. Beat butter until very smooth, then add 2 1/2 cups powdered sugar, 1 tablespoon milk, orange juice, orange zest, and salt and mix to combine. Beat in the puree until combined, then add food coloring, if using. Scrape down the sides and bottom of the bowl, then turn mixer to high and beat 3 to 4 minutes, until very fluffy. Add additional powdered sugar if frosting is too thin and additional milk if frosting is too thick. Frost and decorate cupcakes as desired.