I absolutely love FBCTs. I use them a good bit when people want standard cakes. They are easy to make and edible. I think that's the best way to have a cake be. :)
Step One: I Google 'Coloring Pages' for what I'm looking for. I find a pic I like and print it out.
Step Two: I trace over the picture with a black sharpie. I flip it over and tape it to a cutting board and tape wax paper over it.
Step Three: Outline the picture with black buttercream or whatever you wish.
Step Four: Fill in with the colored icing.
Step Five: After it is filled in with the colors I go over it with icing some more to even some of the thinner spots out and freeze it.
Step Six: Freeze it for at least an hour, take it out and place it on the cake.
Step Seven: You can either build the icing up to make the level of the picture or you can put a decorative trim around it.
Here is another example of building the icing up.
Here is an example of putting trim around it.
And one more example of the trim.
And that's it! It's always good to practice one. The first one I did was a rainbow for a rainbow cake. The sky is the limit for pictures to use.