Yields 12 cupcakes
Preheat oven to 350° F. Grease or line 12 muffin cups.
Combine flour, baking powder, baking soda and salt and set aside.
Cream together butter and sugar. Add zest, juice and food coloring and stir until smooth.
Add eggs and continue to beat until well combined.
Add flour mixture and milk alternately stirring to mix.
Fill muffin cups 2/3 full. Do not overfill or the cupcake tops will spread too far before rising. Bake for 18-20 minutes.
To make Ruby Red Grapefruit Frosting, beat butter and cream cheese together until smooth. Add juice and zest and beat again.
Add powdered sugar, a cup at a time, and beat after each addition until of a spreadable consistency.
Allow cupcakes to cool completely before frosting with Ruby Red Grapefruit Frosting.