Decorate cake. Using ruler and toothpick, divide cake into 7 strips. Each strip should be about 1-3/4 in. wide.
Prepare seven decorating bags, separately, with bright blue, light green, bright yellow, bright orange, bright pink, bright purple and blue buttercream. Cut about 1/2 in. off tip of each bag.
Starting at bottom with bright blue, fill in strips of cake. Use angled spatula to smooth and blend colors.
Prepare decorating bag with tip 3 and black icing. Pipe animal print on cake.