1. Preheat oven to 325°. Beat butter and shortening at medium speed with a heavy-duty electric stand mixer until creamy. Gradually add sugar, beating until light and fluffy. Add eggs, 1 at a time, beating just until blended after each addition.
2. Stir together flour and next 2 ingredients. Add to butter mixture alternately with milk, beginning and ending with flour mixture. Beat at low speed just until blended after each addition. Stir in vanilla. Transfer 2 1/2 cups batter to a 2-qt. bowl; stir in cocoa and food coloring.
3. Drop 2 scoops of plain batter into a greased and floured 10-inch (16-cup) Bundt pan, using a small cookie scoop (about 1 1/2 inches); top with 1 scoop of red velvet batter. Repeat around entire pan, covering bottom completely. Continue layering batters in pan as directed until all batter is used.
4. Bake at 325° for 1 hour to 1 hour and 5 minutes or until a long wooden pick inserted in center comes out clean. Cool in pan on a wire rack 10 minutes; remove from pan to wire rack, and cool completely (about 1 hour). Drizzle with Snowy White Vanilla Glaze.
Total time includes glaze.