I had just ordered her a Hello Kitty shirt for her birthday which, ironically, had a rainbow on it. 
My husband had shown me some tie dye cupcakes online and it triggered the memory of this AMAZING rainbow cake I had filed away to try sometime. No doubt this was the perfect choice for my girl! The only problem... I came up with this idea the day before her birthday. It was crunch time!!! I was able to find an excellent tutorial video which helped me through the process. It is a must watch if you want to attempt this! I opted for the easy way out because of my time constraints. Duncan Hines white cake mix and frosting saved the day! I separated the batter equally into six different bowls and added Wilton food coloring GEL to give it the rich, vibrant color. (According to the tutorial food coloring liquid is not as effective so I made the splurge!) Red was the most difficult color to create. It was very pink. I may have dumped half the bottle of gel in by the time all was said and done but thankfully after it came out of the oven it had turned into a bright red. Some of my cakes stuck to the pan, but as noted in the tutorial I just filled the pieces back in and it didn't show in the layers (just like they said!). I also used some of my handy tips from my SweetWise class to "torte" the cake (cut it across the top to make it even) and most importantly mash the cake down in trouble spots. I love this tip. Kathy said, "Most people think cake is so fragile. It's really not. If there's a part sticking up just push down on it." There was a bit of cutting and mashing to make the layers even. See the building process below:
You can tell this cake was very tall. I used 2 box mixes and 3.5 cans of frosting. This was time consuming and truly a labor of love. But, it was all worth it! 
As an added bonus, the cake tasted surprisingly AMAZING. I'm guessing it was the frosting ribboned in between the layers that made the difference. But, she almost ate her entire 6 layer piece and the next morning asked me for cake at breakfast. Denied. But made me feel good that she remembered it and loved it. Happy Birthday Cherr Bear!
