Rainbow Cake, I Want You!

Kristen brought this rainbow cake to my attention in the comments section and I felt like it needed some more attention. Let me just say that I have been dreaming about it. Enrique and I were supposed to be hosting a party next week, and he has recently crushed my dreams of that happening, so I am looking for a good excuse to make this for some occasion. Do you live in DC and want a cake? I can make that happen.
I finally read the recipe today. I am totally making this cake, but not with any of the ingredients they recommend. It is a diet cake, which is fine, but no way am I using fake whip cream, soda, and/or instant jello. Once you have actually whipped some cream, I don't know why you would ever go back to the tub (well in this case because it is a diet cake, so I guess I do understand that). I want to make a real (non-diet) cake but use this color method to also make it a rainbow.
Anyway. The woman who wrote this blog has a FAQ section at the bottom of the post regarding the cake. I like her attitude.

Photo Source

FAQ
Here are questions I get over and over again about this cake. I just don’t want to answer any more emails about it. These questions apply to any cake, so please don’t blame your epic fail on me.

Omg my cake burnt! 
Next time don’t bake it for as long.

My cake stuck to the pan!
Grease your pan better next time.

My cake burnt/stuck to the pan/was underdone/crumbled. Is this because of the food colouring I used?
No, the food colouring has nothing to do with the failure of your cake. You baked it too long/didn’t grease enough/didn’t bake long enough/moved it before it was cool.

I’m making this for my kids, can I use non-diet soda for this cake?
I don’t know why you would, you certainly wouldn’t be saving much in the way of calories, and I don’t really think your kids need more sugar. Just make a regular cake and then put food colouring in it, it will look the same, promise.

If I don’t make it with soda, will the colours run?
No. In fact, like I keep saying, please just use whatever the hell cake recipe you like. Please. The rainbow part has nothing to do with Weight Watchers.

The frosting, it’s so thick!
Yes, buy a tub of Duncan Hines frosting as a backup plan.

The cake, it fell apart!
Let it cool before you move it, and more importantly, don’t jostle the thing about.

I don’t like the cake this made, blech!
You probably aren’t on a diet, so I don’t know why you bothered to make diet cake.

I don’t get it, you make two cakes and then you put them on top of each other?!
Yes, it’s called a layer cake, and pretty much any cake you buy at a grocery store is constructed in the same manner.

But I don’t *like* food colouring.
Well, you’re wasting your time reading this, aren’t you?

ha.