Preheat oven to 350°F. Spray ribbon cake pan with vegetable pan spray.
In large bowl, combine cake mix, sour cream, egg whites, vegetable oil and, if desired, icing color with electric mixer. Beat on high 2 to 3 minutes. Gradually add pureed strawberries. Continue mixing 2 to 3 minutes or until well blended. Divide batter evenly between prepared pans.
Bake 35 to 40 minutes or until cake tester inserted in center is clean when removed. Cool in pan on cooling rack 10 minutes. Remove from pan and cool completely.
Cut cake board to shape; cover with silver fanci-foil. Tint 1-1/4 cups icing pink. Position cooled cake on prepared board. Spatula ice sides smooth with white icing; spatula ice top fold area of ribbon smooth with pink icing. Outline ribbon in pink with tip 4; fill in with tip 16 pink stars. Pipe tip 18 white shells on bottom border.