That would be nice and I've seen rainbow cakes but...how do they get those colours into the actual cake mix? (see how I linked that!)
So I googled that and after a few sites, settled on a site called Omnomicon this gives good information and has piccies too.
I only have two types of food colouring in my pantry at the moment - those liquid ones in the wee plastic bottles and some "candy" colourings (for chocolate).
Apparently there are colours that come in a gel form and they are what you use for colouring cake mix (I know, I know - lots of you knew this already, but I'm only a beginner with some of this and I figure that some of the readers are too).
Here's the colours being mixed in.
Here's the cake mix going into the baking pan (and I have to be honest here - I'm not sure about how it looks, I mean, brightly coloured food, that's just not natural!):
It looks quite okay once baked though.
The baker says that you can use any cake recipe and you don't have to use hers which is a diet one.
If you have the time, you may like to read through the 1664 comments on this cake (who'd have thought this would generate so much controversy)!
Personally, I don't have the time, however I did glance through a few. I really liked this comment which by the way is completely off topic.