Red, White and Blue Marble Layer Cake

Name: Red, White and Blue Marble Layer Cake
Prep time: 10 min
Cook time: 30 min
Total time: 40 min
Cuisine: American
Ingredients: 1 C unsalted butter (softened); 2 C granulated sugar; 6 egg whites (room temperature); 2 tsp vanilla extract; 3/4 tsp salt; 4 tsp baking powder; 3 C cake flour; 1 C milk; Americolor super red food gel color; Americolor royal blue food gel color; 1 1/2 C unsalted butter (softened); 1/2 C shortening; 6 C powdered sugar; 2 Tb heavy cream; Non-pareils for decoration (optional)