Grease and line 2 (six-inch or eight-inch) cake pans. Preheat oven to 325 degrees F.
In a measuring cup, combine 1/4 cup, plus 2 tablespoons of hibiscus tea, with 1/2 of the egg white mixture, pink food coloring and red food coloring. (If you don’t have pink food coloring, you can use 3 drops of red food coloring.) Whisk together and then set aside.
In another measuring cup, combine 1/4 cup, plus 2 tablespoons of milk, with 1/2 of the egg whites mixture and caviar from 1 vanilla bean OR 1 teaspoon vanilla paste. Set aside.
In a stand-up mixer, with the paddle attachment, add the cake flour, unsalted butter, sugar and baking powder and salt. Mix until the butter looks like sandy bits. Divide the butter/flour mixture into two. If you like precision (like I do), you can weight it out. Each bowl of butter/flour mixture should weigh about 302 grams.
To the first bowl of the flour mixture, add the hibiscus/egg white mixture. Mix until the mixture becomes smooth-ish. Adjust the coloring if needed. Pour the hibiscus cake layer batter into one of the prepared cake pans.
To the second bowl of flour mixture, add the milk/vanilla/egg white mixture and mix until the smooth-ish. Pour the vanilla bean cake layer into the second prepared cake pan. Transfer both to the oven and bake for 25 to 30 minutes, until a skewer inserted into the center comes out clean.