Use food coloring to tint the icing so that you have one color to represent the cytoplasm, a second to represent the cell membrane, and a third to represent the nucleus.
Pro Tip: Start with white frosting and use colors that mix easily to form new colors. That way, you don't have to divide icing and guesstimate how much you'll need for each cell part.
Add a few drops of food coloring to the vanilla frosting and mix well to create the cytoplasm. Frost only the top of the cake.
Next, add a few drops of food coloring (using a different color) to tint the icing a different shade (green pictured). Frost only the sides of the cake with the second color. This color represents the cell membrane.
Finally, add a few more drops of food coloring to the remaining icing to create a third color to represent the nucleus. We chose to add red, which created a rather unappetizing color. Just something to think about.
Cut the top off the cupcake. Place it on the top of the cake to represent the nucleus and frost it with the third color.
You can discard the bottom of the cupcake if you choose. However, I recommend that you put a little leftover icing on it and eat it while your kids aren’t looking!