A little while ago I finally had the chance to use food colouring in my cake recipes, which turned out quite cool, though some people dislike mostly the green and blue coloured cakes.
To make fancy coloured muffins is not so hard. In my case I lazily used a pack of mixture from the shops that describes how you can easily make the muffins. Once you've made the dough, simply add the colouring. On the internet they like to use 'gel' colours, but they are hard to get outside America. Liquid colouring, as I used (found at a Toko) also works fine.
Here are some pics of my first attempt of making coloured cakes
"A room without books is like a body without a soul" - Cicero
Unfortunately not now (don't think you would've wanted that... as they were made some weeks ago, haha)
Anyway, may there ever be an international meeting of some sort, I'll make some cakes
"A room without books is like a body without a soul" - Cicero
Food colouring can also be applied to other foods. I once visited a classmate's frat house where he showed me their mayonnaise. They actually coloured it blue. This was done as a joke to freak out unsuspected guests. Although the mess in the kitchen was enough to freak me out beforehand.