Preheat the oven to 350°F and line a 12-cup muffin pan with paper cupcake liners.
In a large mixing bowl, beat the unsalted butter and granulated sugar with a hand mixer or stand mixer on medium speed for 3 to 4 minutes until very light, pale, and fluffy.
Add the sour cream, vanilla bean paste, and 1/2 tablespoon orange zest to the bowl and mix on low speed until fully combined and creamy.
Add the egg whites in 2 additions, mixing on low speed after each just until incorporated; do not overmix.
In a separate bowl, whisk together the flour, baking powder, and salt until evenly combined.
Add one third of the flour mixture to the butter mixture and mix on low just until combined.
Stir together the 1/4 cup orange juice, 2 tablespoons citrus juice, and milk in a small measuring cup.
Add half of the juice and milk mixture to the bowl and mix on low until combined.
Add another third of the flour mixture and mix on low, then add the remaining juice and milk mixture and mix again just until the batter is smooth.
Add the final third of the flour mixture and mix on low speed only until no dry streaks remain; the batter should be soft and thick.
Divide the batter evenly among the 12 liners, filling each about two thirds full.
Bake for 14 to 16 minutes, or until the tops are lightly golden, spring back when gently touched, and a toothpick inserted in the center comes out clean.
Let the cupcakes cool in the pan for 5 minutes, then transfer them to a wire rack to cool completely before frosting.
While the cupcakes cool, place the salted butter and shortening in a large bowl and beat on medium speed for 3 to 4 minutes until creamy, pale, and slightly fluffy.
Gradually add the confectioners’ sugar, about 1 cup at a time, mixing on low speed after each addition until incorporated, then increasing to medium speed until smooth.
Add 1 tablespoon citrus juice, 1 teaspoon orange zest, and 2 teaspoons orange juice to the frosting and beat on medium speed for 2 to 3 minutes until light, smooth, and fluffy.
If desired, transfer half of the frosting to a separate bowl and tint lightly with a small amount of orange icing color, mixing until the color is even.
Fit a piping bag with a large star tip and fill it with both the plain and orange tinted frosting side by side to create a sunrise swirl effect.
Pipe generous swirls of frosting on each cooled cupcake, starting at the outer edge and spiraling inward and upward.
Drizzle about 1/2 teaspoon grenadine over the top of each frosted cupcake so it slowly sinks and lightly tints the frosting.
Garnish each cupcake with a cherry and a small orange wedge, if using, and serve immediately or store covered until ready to serve.