Cream butter and sugar in a large bowl. Add eggs, one at a time, beating well after each addition. Add vanilla, milk, and sour cream. Beat well.
Sift in cake mix; beat on low speed until incorporated. Sift in cake flour; beat on low speed until incorporated. Finish folding ingredients with a wooden spoon or rubber spatula to ensure that all ingredients are well combined.
Preheat oven to 350°F. Thoroughly grease a 10- to 12-cup Bundt pan, or spray with nonstick baking spray.
Spoon a layer of orange, green, purple, orange, green, and purple batter into bottom of bundt pan. Carefully swirl with butter knife. Tap pan several times on counter to evenly distribute.
Bake at 350° F for 50 to 55 minutes, or until toothpick inserted into the center comes out clean.
Remove from oven; let cake cool in pan for 10 minutes. Invert cake on wire rack; cool completely.
Beat cream cheese, cream, and vanilla in a medium bowl until smooth. Add confectioners' sugar; beat until smooth.
Spoon cream cheese frosting around top of cake, allowing frosting to drip down the sides. Sprinkle top with Halloween sprinkles. Top with half candy pumpkins.
Yield: 12 servings.