Preheat oven to 350 degrees.
Cream butter and sugar for 5 minutes. Add eggs one at a time, making sure they are well incorporated before you add another egg.
Mix in vanilla extract and orange zest. Combine flour and baking powder then mix. Slowly add flour and mix until well combined.
Pour into a greased 9 inch cake pan that's been line with parchment paper and bake at 350 degrees for 35 minutes. Cake should spring back when gently touched. Remove from oven and allow to cool for 10 minutes before removing from pan.
Once the cake is out of the pan, remove the parchment paper and discard. Allow cake to cool on a rack before serving.
*Optional. To achieve this color combination I colored 1 cup of batter red and one cup green. I alternately dropped the red, green and uncolored batter into the cake pan. I then swirled the batters together with a knife.
