Here is a picture of the batter before baking:
Looks great, right?
Well, the cakes baked several inches out of the jars & all of the colors blended together. Lesson learned - fill jars no more than a third to a half of the way & choose drastically different colors for multiple layers.
In an attempt to salvage the project, I cut each cake cylinder and assembled these mini rainbow cakes in jars:
And the leftover pieces in tupperware...at least they taste good!