Preheat oven to 350°F. Grease and flour two 8- or 9-inch round pans.
Combine cake mix, water, oil and eggs in large bowl. Beat at low speed with electric mixer until moistened (about 30 seconds). Beat at medium speed for 2 minutes. Divide batter in half (approximately 2 1/4 cups each). Blend blue food coloring into one portion, or until desired shade is reached. Blend yellow food coloring into the other portion, or until desired shade is reached. Pour blue batter in one pan and yellow batter in the other.
Bake and cool cakes according to package directions.
To assemble, place blue cake layer on serving plate. Spread lemon curd on top of layer. Top with yellow cake layer. Spread frosting on top and sides of cake. Decorate with candies. Garnish with fresh lemon peels or slices if desired.