Preheat oven to 350°F. Line muffin pan with 12 liners (more on another pan if needed) and set aside.
In a large bowl, cream together butter and sugar until light and fluffy. Add eggs and beat well.
In a separate medium bowl, whisk together 1 ¾ flour, baking soda, baking powder and salt - set aside.
In a small bowl, whisk together Sprite/7Up and sour cream.
Add half of flour mixture to butter mixture, beating well. Add soda mixture, beat well, and then add the rest of the flour mixture. Beat until well combined.
Pour 1 cup of batter into a small bowl and add ¼ cup flour, cherry juice and grenadine. Mix well with a whisk. Add red food coloring a drop at a time until desired color is reached.
Add a tablespoon of colored batter mix to the bottom of each cupcake liner, spreading so that the batter is leveled. Using a ¼ measuring cup, pour the remaining batter on top of the colored batter to fill cups ¾ full. Instead of leaving the colors separate, you could also use a toothpick to swirl the batter.
Bake for 17-20 minutes until the tops of the cupcakes are set and a toothpick inserted into the center comes out clean. Let cool in pan for a couple minutes and then move to wire rack to cool completely.