Preheat your oven to 325°F (165°C) and generously grease a 10-cup bundt pan with baker's release.
In a stand mixer with a paddle attachment, cream the room-temperature butter and granulated sugar until light and fluffy.
Gradually add the egg whites and vanilla extract, mixing until just combined.
Gently fold in the all-purpose flour until a thick, dense pound cake batter forms.
Divide the batter evenly into three separate bowls. Color one bowl with red gel food coloring, one with blue gel food coloring, and leave the third white.
Dollop the red, white, and blue batters alternately into the prepared bundt pan. Use a knife to gently swirl the colors together, being careful not to over-mix into purple.
Bake for 50-60 minutes, or until a toothpick inserted into the center comes out clean.
Let the cake cool in the pan on a wire cooling rack for 10 minutes before carefully inverting it onto a plate.
Whisk the powdered sugar with milk to create a bright white glaze, then drizzle over the completely cooled cake.
Top with patriotic sprinkles and serve alongside fresh strawberries, blueberries, and whipped cream.