Preheat oven to 350°F. Prepare cake mix as directed on package, adding vanilla. Divide batter evenly into 2 bowls. Stir blue food color into one bowl. Stir purple food color into second bowl. Alternating colors, drop heaping spoonfuls of batter randomly into greased 13x9-inch baking dish.
Bake 30 to 40 minutes or until toothpick inserted in center comes out clean. Cool completely in pan.
Poke large holes all over cake using the end of a wooden spoon. After holes are made, mix milk and raspberry extract in large bowl. Add pudding mix; stir just until mixture begins to thicken. Immediately pour pudding over cake, filling the holes.
Frost cake with whipped topping. Refrigerate at least 1 hour or until ready to serve.