It is not super hard really. I followed the directions on a box of Fun-fetti cake mix, split it into two bowls and added brightly colored food coloring. I did this with two boxes of cake mix, so the cake was super tall. I whipped up a white icing and sprinkled it with colored sugar crystals on top. I thought it would be a big process, but it was one of the easiest cakes I have ever made! She was so surprised when I cut into the cake and it was all bright with color. Give it a try!
*just a note: The cakes will appear to be brown in the oven. You might even think the color did not take or that it will look burned. But, the inside is where the vibrance hides! So, use a toothpick and dig around to see if it is the color you were going for.