Preheat oven to 350F degrees.
Spray a 9"x 13" baking dish with nonstick spray.
In a medium bowl, combine dry cake mix with dry instant pistachio pudding. Mix those together until combined.
Then add in eggs, oil and milk. Stir just until combined.
Stir in about 6 to 8 drops of green food coloring until fully incorporated. Pour into prepared baking dish.
Bake for about 25-30 minutes. If you insert a toothpick into it, it should come out clean when done.
Allow cake to cool completely before making frosting.