Your batter is going to be lumpy. But it's okay. Just mix it up according to the box directions. And you can take licks of this! No raw eggs!
Here's where I suck because I didn't get any of the dividing-the-batter action. (Sorry the pictures is a little blurry!) I knew I only wanted 3 colors so I basically figured out how many ounces were in the whole thing and divided it by 3, then put the batter in 3 separate bowls. I added the gel color until it was the color I wanted.
I don't know how I got perfect circles in my cake but here is how I layered it. I knew I wanted the bottom color to be the most prominent so I put about 2 and half cups of the bottom color in first. Then I put about 1 1/2 cups of the second color and about 3/4 cups of the third color. Eyeball it and trust your gut.Then bake that sucker according to the directions on the box. Mine required an extra 10 minutes or so. Just keep poking it with a toothpick until it comes out clean. The tops of my cakes were really bloated so I shaved the entire bump off the bottom layer and part of it on the top. Now it's time for FROSTING!
All you're going to do here is take 16 oz. of cool whip and mix in the two packages of fat-free, sugar-free pudding (I used the white chocolate flavor). I would do it one at a time. It makes it a little easier to mix. Also, I would mix this while your cake is baking. That way the whip cream has time to thaw out. That will come in handy later.