Preheat oven to 325°F. Prepare a large bundt pan with butter and flour or by spraying with non-stick spray. (My 10-inch bundt pan is 3 inches deep. There should be at least 1 1/2 inches between the height of the batter and the top edge of the pan.)
In the bowl of a stand mixer fitted with the paddle attachment, combine cream cheese and butter until smooth, about 3 minutes.
Gradually add the sugar and mix until light and fluffy.
Add the eggs, one at a time, mixing well after each addition, followed by the vanilla.
Slowly add the cake flour and cocoa powder. Mix until combined.
Remove bowl from stand mixer and pour in the buttermilk. Mix by hand until just incorporated. Use a rubber spatula to scrape the sides of the bowl to get every last bit of ingredient incorporated.
Fold in the food coloring, one teaspoon at a time, until the desired color is reached.
Pour batter into prepared bundt pan. Bake for 1 hour to 1 hour and 20 minutes. Check for doneness at 1 hour. (The cake is done when a toothpick inserted into the center of the cake comes out with a few crumbs, but no wet batter.)
Allow cake to cool to room temperature before inverting on a plate and adding frosting.