White cake mix (for 2 layer cake)
2 packages cherry Kool-Aid type drink mix
White frosting
1 cup granulated sugar
Green food coloring
1/3 cup raisins
Flour
Ingredients according to cake mix directions (water, oil, eggs, etc.)
Oven safe Pyrex mixing bowl

Preheat oven to 350 degrees F. Grease and flour oven safe mixing bowl. Be sure that your bowl is completely oven safe. It must say it right on the bowl to be assured of being oven safe. Most glass bowls are not oven safe.

Put cake mix in another bowl with 2 packages of Kool-Aid type drink mix and 1 cup of sugar; stir to combine. Add ingredients listed on cake mix package and mix as directed.

Roll raisins in flour and add to finished cake mix (just raisins not any extra flour). Pour into oven safe bowl. Bake 50 to 55 minutes. Checking every 5 minutes after 40 minutes. Check for doneness with knife inserted in center of cake. When it comes out clean the cake is done. Remove from oven. Let stand 10 to 15 minutes before inverting onto cake plate to remove cake. Let cool completely. 

Stir green food coloring into frosting a few drops at a time to make a nice light green. Frost cake, bringing spatula from the bottom to the center (the unevenness of the frosting will resemble where the vine was attached to the watermelon. Squeeze a few drops of food coloring onto a small dish. Dip tip of your frosting spatula into the color and onto the cake in a radial pattern. Do this around the whole cake. Don't worry if streaks are too dark; when you do the next step they will lighten up and, besides, the streakier the better for a watermelon cake. Starting at sides of cake run spatula all the way up the cake and almost to the center and then stop. Repeat this all the way around the cake.