Isn't this the prettiest cake?! I just love it!! The kids and I made this for St. Patrick's Day and had a lot of fun doing it. My sister sent me a link to this great idea here and I sort of modified the recipe a bit for us.
First, start with a couple of white cake mixes. Or in our case, a *classic white* and a *French vanilla*, since that was what I had:) Just make the mixes as directed on the box, combining them in one bowl.
Next, divide your cake batter evenly into 6 smaller bowls. You're going to put {approximately} 1-1/2 cups of batter per bowl. Then dye each bowl a different color. I suppose you could get crazy with the colors, but we went with the traditional rainbow colors.
I used gel food colors for the first time and really liked them. They were easy for the kids to use, too.
Then you start pouring your batter into your cake pans. WAIT! Don't forget to grease and flour your cake pans (like I did!). This is important, even if you're using brand new non-stick pans (trust me!). For the first pan begin with one end of the rainbow (purple) and work toward the red, pouring about 3/4 cup of batter into the center of the pan and then each subsequent color directly on top of the last. Don't spread the batter, let it do it's own thing. 
For the second cake pan start on the red end of the rainbow and work toward the purple. You're going to love this part! The batter was so pretty!!
This is what your two full pans of batter will look like, approximately. Now, notice that one of my pans is more full than the other. Don't do that! I've adjusted the measurements for you though, so that shouldn't happen to you (you can thank me later:).
See?! Even the empty batter bowls look pretty!
Here is why you don't want to get one pan too full: one of my cake pans ran over. Luckily, I figured this would happen so I put a cookie sheet under it. Don't worry though, the cake that dripped out baked just fine and we ate that part, too...heehee
Finally, after your cake layers have cooled, it's time for the frosting. You can use whatever frosting you like. Let me tell you about this little favorite of ours. It's just white chocolate (or whatever flavor pudding you like) pudding mix and whipping cream. Yeah, no fat there, whatsoever. You simply pour the mix into a mixing bowl, followed by the whipping cream. Then beat it together and it comes together in just a jiffy. And it's AMAZING!! The ratio is 1 small box of pudding mix to every 8 oz. of whipping cream. This cake took 4 boxes...let's not discuss how much whipping cream that is.
Here's the finished product. Kind of plain looking on the outside, huh? I wanted to use sprinkles, but my husband is against those. So I let the cake speak for itself instead.
And speak it did! Look at that color! I have to say this is maybe the most fun I've ever had baking a cake. Just because it's SOOOO pretty!!Oh~and it tastes great, too!
