Prepare the Striped Vanilla Cake:
Preheat oven to 325°F. Grease and flour 3 6-inch cake pans.
In a medium bowl, whisk together buttermilk, sour cream, vanilla, egg whites, and vegetable oil. Sift in cake mix and stir until just combined.
Spoon 1/3 of the batter into the first prepared pan.
Add a small amount of red gel food coloring to the remaining batter, stir to make it pink, and divide it between two more prepared pans.
Add a few drops of red coloring to the final batter portion for a red hue, and spoon it into the last pan.
Bake for 25-27 minutes. Allow to cool for 2 minutes, then flip out onto a cooling rack to cool completely. Wrap in plastic and freeze to make frosting easier.
Prepare the White Chocolate Raspberry Buttercream:
Microwave white chocolate chips with 1/4 cup heavy cream for 30 seconds. Stir until smooth, then set aside.
Whip the softened butter in a stand mixer on high speed until light and fluffy.
Add the chocolate ganache, pinch of salt, vanilla, and raspberry emulsion. Mix to combine.
Add the remaining 1/4 cup heavy cream, then gradually add sifted powdered sugar, 1/2 cup at a time. Continue mixing until smooth and fluffy.
Prepare the Pink Ganache Drip:
In a microwave-safe bowl, combine white chocolate melts and heavy cream. Microwave for 30 seconds, stir, and repeat until smooth.
Add a tiny bit of red gel food coloring to achieve a pastel pink color. Stir well and set aside.
Assemble the Cake:
Slice each of the three cake rounds in half to create 6 layers: 2 red, 2 pink, and 2 white.
Place the first red cake layer on a cake board and pipe a thin layer of buttercream on top. Add the pink layer and repeat with the buttercream. Continue with the remaining layers (white, pink, red).
Crumb coat the cake and freeze for 5 minutes.
Apply the final layer of buttercream. Press sprinkles along the bottom edge.
Add the pink ganache drip, and return the cake to the freezer for 5 minutes to set.
Top with chocolate bark, fondant hearts, gumballs, roses, and sprinkles.