|Thanks for the pic Jeanelle :)|
Most of the rainbow cake recipes I found online had recommended using gel food colouring instead of liquid, as the colours supposedly turn out more vibrant. Unfortunately, I had no idea where to get gel food colouring and so stuck with good ole' Queens liquid food colouring.
However, I had read somewhere that the trick to maintaining a vibrant colour was to add vinegar, which I obeyed, and hoped for the best.
I had to do some alchemy to get purple and orange, but thanks to D's wonderful mathematical skills, that wasn't too hard.
Purple: three parts red, one part blue
Orange: one part red, two parts yellow
I used a simple white cake recipe for the batter and just separated them evenly by six before I added the food colouring. What I did wrong however, was to put them in the oven for the same time indicated in the recipe. With each individual colour being such thin layers, I could have left them in for about half the time and ended up with a cake that would have been more moist.
However, it wasn't a problem that sweet icing couldn't cure!