Rainbow cake's in the oven as I type this ... the purple and blue layers are done, and green's a-baking ... I had to use generous drops of liquid food colouring as I couldn't find the gel type [which is said to give far more bright colours]. I'm going to do the remaining layers later, and ice them - frost them? - tomorrow. I'll put some pics up too. Yay!
And now I must scoot and do some assessments.
Edit: If anyone missed it, the recipe for rainbow cake is here. And I used Betty Crocker's Super Moist Vanilla Cake mix for the base.