First split your buttercream icing into separate bowls (6 Bowls) then mix your food colouring into the bowls. (Each bowl has different icing)
Split the icing evenly into different bowls.
Remember to mix all the colouring through.
Then collect your cupcake you would like to use (I have used a rainbow cupcake)
Then slice the top of the cupcake off (just so you can place the icing evenly)
Now ice the bottom layer of the cupcake in a purple icing you have prepared before, continue to layer the cupcake going from the bottom (purple, blue, green, yellow, orange)
At the top of the cupcake place a red Jaffa ontop of the orange icing.
The rest of the rainbow cupcakes you can customise yourself! Have fun doing this (I sure did!)