Preheat waffle iron to medium-high heat setting.
Mix flour, cocoa powder, sugar, baking powder, salt.
Whisk eggs, buttermilk, butter, vanilla in separate bowl.
Combine wet and dry ingredients until just mixed.
Divide batter into two equal portions carefully.
Add red food coloring and vinegar to one.
Swirl batters together gently for marble effect.
Pour batter onto preheated waffle iron immediately.
Cook for 4-5 minutes until golden brown.
Serve hot with your favorite toppings immediately.