We recently were inspired by momstown Barrie's rainbow birthday bash for her daughter and tried the multi-coloured cake ourselves. What a simple process with terrific results!
Start off with a white cake mix and follow the directions to prepare. Once ready, divide into various bowls, depending how many colours you want. We split it into four bowls and added a different food colouring to each. (Notice the serious mixing duty here from my sous chef with his tongue pointing out!)
Once mixed, pour the coloured batter into greased cake pans. This is a bit of an experiment. My kids were SO excited to see what would happen and if the colours would blend (they didn't).
Once baked, ice the cake as usual and decorate. We used multi-coloured candies to create an easy rainbow. When you cut the cake, the colours are vibrant and fabulous! It still tastes like it's a white cake which is a bit of visual trickery! The same effects would be incredible for cupcakes too, a little more tedious but worth the time to create mini rainbows.
Happy St Patrick's Day and may you see a rainbow with a pot of gold!