In the end, I decided on this beauty:
Oh yeah, I did mention it was a RAINBOW cake...
Pre-cooked cake batter. Yum.
There are lots of rainbow cake and rainbow cake recipes out there, this, I believe, being the original. But I'll go ahead and give you a brief run down here, the cake is that easy.
1 box of Cake Mix (or any other cake recipe, really) that is white or close to in color.
1 package of food coloring GELS. The GELS part is important, capitalized for emphasis of importance.
Frosting, decorations, etc, are completely optional. For tips on the rice crispy Dragon and marshmallow castle, scroll to the bottom.
Basically, follow the directions for the Cake Mix accordingly, though I highly recommend substituting oil for a proportional amount of apple sauce (not only is the cake healthier this way, but more moist). If you're using a plain white cake mix and want some flavor, add a tablespoon of any extract you desire (I used raspberry). Next you can either bring out six smaller bowls or just one bowl that you continually clean between each coloring because you're a masochist like that. In each bowl pour equal amounts of batter (or if using the same bowl, I recommend using a measuring cup) and then mix in the appropriate gel coloring.
You should use gel instead of regular food coloring because gel colors are much more intense and will result in a cake that looks like this:
The colors are even brighter in person, I kid you not.
Layer each color ONE AT A TIME. I recommend smoothing the first layer with a spatual so it covers the entire bottom before dumping the next layer on. Do your best not to mix the layers together so the colors do not mix into some angry brown glob.
If you used apple sauce instead of oil, after the cake has cooled you will want to place it in the fridge for a bit so the frosting is less likely to tear the top of your very, all over moist cake.
Marshmallow Castle tips:
Oh dear God that castle...it was so difficult and turned out so ugly. Maybe you'll fare better than me.
-Marshmallows were dipped in water, then immediately rolled into gray sugar crystals, then set on wax paper to dry.
-A bajillion toothpicks were used to hold up this castle.
-Unlike what I did, BUILD YOUR CASTLE ON A FLAT SURFACE IN ORDER TO REDUCE LEAN!!!!
And now...the DRAGON.
The dragon was made using a basic rice crispy treat recipe with green food coloring. I recommend making extra just in case you accidentally break your dragon in your mouth and need to make another. Let the cereal mixture cool a little before dumping globs of it into sheets of wax paper. If the mixture is too warm, it will stick mostly to the paper and be hard to sculpt. Too cold and, well, it will be hard to scoop out of the pot.
Let the treats cool completely inside of the wax paper. The treats should still be sticky enough after cooling to assemble like so: