Cut the heads off of the cakes so that they are all the same size flat on top.
Then place icing on the bottom layer and add another layer and continue to do that until you have four layers perfectly stacked on top of each other.
Place the cake in the fridge for about 15min to allow the buttercream to harden slightly.
Then apply a thin layer of icing around the whole cake (crumb coat), and place the cake back in the fridge for at least another 20min.
To create the ombre effect, divide the remaining buttercream into 4 different bowls.
Mix in 3 different types of food colouring into each one, leaving the last bowl with the original white buttercream.
Remove the cake from the fridge, then starting at the bottom, place the darkest shade of pink roughly around the bottom of the cake (using a piping bag or spatula).
Then add the second shade, then the third and lastly place the remaining white buttercream on the top of the cake.
Then using either a smooth cake scraper or a large offset spatula, gently smooth the cake around, taking off all the excess icing. The colours will start to blend into each other slightly.
Continue to do so until the cake has a smooth appearance.
Place cake in fridge or serve immediately.