Heat oven to 350℉.
Spray four 6 inch cake pans with baking spray. Set aside.
In a large bowl, whisk together flour, sugar, baking powder, and salt.
In a medium bowl, whisk together milk, eggs, vegetable oil, and vanilla.
Pour wet ingredients over dry ingredients.
Mix only to blend.
Stir in white chocolate.
Divide batter in half.
To one half of the batter, add dye.
Stir until incorporated.
Divide plain batter evenly between 2 of the prepared pans.
Divide red batter evenly between the other 2 prepared pans.
Bake for 25-30 minutes, or until cake tests done.
Allow to cool 5-10 minutes, or until pans are cool to the touch.
Turn out on wire cooling rack. Cool completely.
Level, if needed.