I have always had a strange obsession with Rainbow's so I made Rainbow Jello. Totally time consuming and hardly worth it, but it made my day so here it is:
I am sure you get the idea of how this is done but just get all the colors of Jello that you want. Make the first flavor and add a small amount to clear cups, allow to solidify. Then add the next color and so on. Seriously it takes like all day. Haha. I think I am the only one who truly appreciated it.