Preheat oven to 350F and line a muffin pan with cupcake liners.
Whisk together flour, baking powder, and salt in a bowl.
In a separate bowl, blend together egg, oil, sugar, vanilla extract, and milk.
Blend the wet mixture into the dry ingredients.
Blend in 1-2 drops of green food coloring or until desired color is achieved.
Divide the batter into the muffin pan and bake for 20-25 minutes.
Meanwhile, blend together the butter, watermelon essence, and powdered sugar. Blend in a few drops of red food coloring until desired color is achieved.
Take muffins out of the oven and leave to cool.
Top with frosting and chocolate chips.