Preheat the oven to 350 degrees F.
Grease a 10-12 cup Bundt cake pan. Set aside.
Drain the strawberries through a fine mesh sieve into a small bowl. Reserve the liquid. Pour the strawberries into a medium bowl. Add a few drops of red coloring if desired. (Strawberries will oxidize while baking.) Set aside.
In a stand mixer fitted with the paddle attachment, add the cake mix, pudding mix, cake flour, and sugar. Mix on low for about 20 to 30 seconds.
Add the vanilla, sour cream, oil, egg whites, and milk. Mix on low until the ingredients are just moistening, about 15 to 20 seconds.
Increase the speed to medium and mix for 2 minutes, scraping the bowl and paddle blade as needed.
After the batter has mixed for 2 minutes, pour about a third of the batter into the bowl with the strawberries and blend together.
Pour about ⅓ of the white cake batter into the bottom of the greased Bundt pan. Dollop the strawberry batter over the white batter.
Pour the remaining white batter over the strawberry layer. Smooth the top. If preferred, you can use the handle of a spoon to swirl, or you can leave the layers as they are.
Bake in the preheated oven for 35 to 45 minutes. Begin testing for doneness with a toothpick at 35 minutes, especially if your oven runs on the hotter side. Bake until the toothpick comes out with just a few crumbs attached.
Remove the pan from the oven and set it on a heat-proof surface; allow to cool for 20 minutes.
Invert the warm cake onto a cake stand/platter and allow it to completely cool if frosting.
The cake may be served warm if just a dusting of powdered sugar is used.
Any leftovers may be kept in an air-tight container at room temperature or refrigerated for 4 days. The cake may be frozen, well-wrapped without frosting for up to 3 months. Thaw then frost is previously frozen.