1. Preheat your oven to 350°F (175°C) and lightly grease mini Bundt pans.
2. In a bowl, sift together the flour, 3/4 cup sugar, and salt; set aside.
3. In a large mixing bowl, whip the egg whites on medium speed until frothy. Add cream of tartar and vanilla extract.
4. Gradually increase to high speed, adding the remaining sugar slowly until stiff peaks form.
5. Gently fold the flour mixture into the egg whites, being careful not to deflate the batter.
6. Divide the batter into three bowls. Color one with red food coloring and another with blue, leaving the third one white.
7. Layer the colored batters into the prepared Bundt pans and swirl lightly with a toothpick for a marbled effect.
8. Bake for 18-22 minutes or until a toothpick inserted comes out clean.
9. Cool the cakes in the pans for 10 minutes before inverting onto wire racks to cool completely.
10. Once cooled, layer with whipped topping and arrange strawberries and blueberries on each cake for a patriotic theme.
11. Chill for at least 30 minutes before serving for best flavor.