Preheat your oven to 350°F now.
Grease the bundt pan thoroughly with butter.
Mix flour, baking powder, and salt together.
Beat butter and sugar until light and fluffy.
Add eggs one at a time, beating well.
Pour in vanilla extract and mix completely.
Add dry ingredients alternately with milk.
Divide batter into two equal bowls.
Mix cocoa powder into one bowl thoroughly.
Add orange coloring to the other bowl.
Alternate spoonfuls of each batter in pan.
Swirl gently with knife for marble effect.
Bake for 50-60 minutes until done.
Test with toothpick inserted in center.
Cool in pan for 15 minutes first.
Invert onto cooling rack to cool completely.