So, I was incredibly inspired and intrigued by everyone's rainbow cakes, so I had to make my own!
I followed these instructions: http://www.omnomicon.com/rainbowcake
which were exceptionally helpful, especially since I made this the day before Easter and had already boiled all the eggs in my house! I used a French Vanilla cake mix and a can and a half of diet cherry 7-Up. I also just used regular liquid dyed and did some elementary mixing to get the colors I wanted!
Then, just layered it in the bundt cake and it turned out magical!!! We served it on frosting "clouds". (My husbands idea.)
Thanks all for the inspiration!
Even the crumbs are pretty!