I made this Rainbow cake with my French friend, Lou.
We mixed an ordinary vanilla sponge and divided it into four bowls, adding some food colouring to each. The colours we used were red, green, blue and purple as we were limited by time and number of cake tins. If we had had more time, we would have divided the mixture up some more and mixed a few more colours.
The food colourings we used for the cake were in the form of gels, which I had been given as a present. I would definitely reccomend gel food colourings over liquid ones because they create a much stronger colour and it is easy to make different shades. You only need a tiny bit of the gel food colourings, so this also means that your icing will not go too sloppy.
After the cakes had baked and cooled for a while, we sandwiched the layers together with cream cheese icing. The icing was left over from a previous cake and I had made it too sloppy, so we stuck skewers through the layers to hold them together. Finally, we sprinkled over some mini smarties. Although it didn’t look too great from the outside, the inside was a completely different story!