Move oven rack to lowest position (remove other racks). Heat oven to 350°F.
In extra-large glass or metal bowl, beat cake mix, water and orange peel with electric mixer on low speed 30 seconds. Beat on medium speed 1 minute. Pour into ungreased 10-inch angel food (tube) cake pan. (Do not use fluted tube cake pan or 9-inch angel food pan or batter will overflow.)
Bake 37 to 47 minutes or until top is dark golden brown and cracks feel very dry and not sticky. Do not underbake. Immediately turn pan upside down onto glass bottle until cake is completely cool, about 2 hours.
Meanwhile, in 2-quart saucepan, mix rhubarb, 1/2 cup granulated sugar and the orange juice. Cook over medium heat 10 minutes, stirring occasionally. Cool 15 minutes. Stir in 1 1/2 cups strawberries. Stir in 4 drops food color if deeper red color is desired. Refrigerate about 1 hour.
In medium bowl, beat whipping cream and 3 tablespoons sugar on high speed until soft peaks form. In large bowl, beat ricotta cheese and 1/4 cup powdered sugar on medium speed until fluffy. Fold in whipped cream.
Run knife around side of pan to loosen cake; remove from pan. Cut cake horizontally to make 3 layers. Fill layers with strawberry-rhubarb filling. Frost side and top of cake with frosting. Arrange 1/2 cup strawberries over top of cake. Store covered in refrigerator.