I saw this idea online in a few places... so I wouldn't know who to credit as the original. So let's just say : this is not MY idea, it came from someone else.
However, i did MAKE this yesterday!! I LOVE how it turned out! I couldn't wait to cut it open and see the rainbow (colors are not in the right order, i KNOW). I just placed them in the order they came out of the oven. I was so amazed with it that I went around and gave slices to my friends! There are no pieces left today!
For the icing, I used the 7-minute icing recipe that Cindy sent me. It is a bit of a merangue type icing. Upon tasting, Maelie, who usually hates most icing, declared that this was the best icing ever! So thanks Cindy for sending it to us!