Rainbow pastel ruffle cake...she just used food coloring, not flavoring and used fondant icing to make the ruffles. I would NOT use fondant which is a pain but settle for buttercream ruffles that don't stand out so much. Still sweet rainbow look.
This video is really helpful and shows you step by step what your cake should look like, the way to put a crumb coat on, the final layer of frosting, and then how to smooth it out with a Viva paper towel. This can get your cake so smooth that it looks like fondant!