I painted it to look like Alphonse (the tadpole) was in a jar like in the story
I used food coloring, paint brushes and water (to water down the food coloring) to paint on top of the white frosting. From reading about it after I started (this was my first time painting a cake) I found out it would have worked much better to have used alcohol like vodka for thinning the food coloring. Then it would have evaporated faster as the water was a little messy and hard to work with. There would have been no alcohol left on the cake once it dried. Some people also use vanilla extract or lemon juice, but both of those would leave flavor. I can't recommend any of these options until I try them myself.
I liked how he turned out and I love the book and highly recommend it!