1. Heat oven to 350 degrees F. Coat two 9-inch round cake pans with nonstick cooking spray. Remove peel from orange with a zester, avoiding pith (about 2-1/2 teaspoons zest). Juice the orange (about 1/3 cup juice).
2. In large bowl, blend brownie mix, eggs, 2 teaspoons of the orange peel, orange juice and oil until well combined, about 1 minute. Divide between prepared pans.
3. Bake at 350 degrees F for 25 minutes, or until toothpick inserted at edge of pan comes out clean. Cool in pans on racks 5 minutes. Invert layers on racks; cool completely.Frosting:
4. In medium-size bowl, beat milk, whipped topping mix and pudding mix on low speed until blended. Increase speed to high; beat 4 minutes or until soft peaks form. Stir in a drop of food coloring and remaining 1/2 teaspoon orange zest.
5. Place one layer on serving platter. Spread with 3/4 cup frosting. Drain mandarin oranges; pat dry. Arrange 3/4 cup orange segments over frosting. Top with second brownie layer. Spread remaining frosting on top and sides of torte. Decoratively place remaining orange segments on top. Refrigerate 1 hour before serving.