Preheat oven to 350°F. Grease two 9-inch-round layer-cake pans. Line bottoms with waxed paper.
Sift together flour, 3/4 cup of sugar, baking powder and salt into large bowl. Add oil, egg yolks, orange rind and juice in order, beating until smooth.
Beat egg whites until foamy. Gradually beat in 3/4 cup sugar until stiff, but not dry, peaks form. Fold into batter just until blended. Pour into prepared pans, dividing equally.
Bake in 350°F oven 30 minutes or until tops spring back when lightly touched. Cool cakes in pans on wire racks for 10 minutes. Invert cakes onto racks and cool completely.
Beat butter in large bowl until fluffy. Gradually beat in 10X sugar until creamy and smooth. Beat in rind, juice, salt and food coloring; if necessary, beat in more orange juice to make good spreading consistency.
Remove waxed paper. Cut each layer in half to make a total of 4 half-moons. Measuring 2 inches along cut edge of each cake from end, cut out notch, 2 inches deep. (Reserve cake notches for snacks.) On a serving platter, place 2 half-moons or wings, rounded sides touching in middle, and notches opposite each other on outside edges. The shape should resemble a butterfly. Spread top of wings with marmalade. Top with remaining 2 wings, lining up notches. Spread top and sides of cake with frosting.
Sprinkle mini chocolate pieces down center between wings for the body. Decorate wings with flowers.