Heat oven to 350℉/177℃.
Spray a 10-cup Bundt pan with baking spray. Set aside.
In a large bowl, combine flour, cocoa, baking powder, baking soda, and salt. Set aside.
Combine butter and sugar in the bowl of a stand mixer fitted with the paddle attachment.
Beat until light and fluffy, about 2-3 minutes.
Mix in dye.
Add eggs, one at a time, beating well after each addition.
Add flour mixture alternately with buttermilk, beginning and ending with flour mixture.
Stir in vanilla and vinegar.
Pour into prepared pan.
Bake for 45-50 minutes, or until cake tests done.
Allow to cool in pan for 10 minutes.
Turn out onto cooling rack to finish cooling.