Add 3 cups boiling water to the 3 boxes of green Jello. Take 1 1/2 cups of Jello out and add 6 tablespoons sour cream. Mix well. Pour in pan. Let harden in refrigerator. To remaining green Jello; add 9 tablespoons cold water. Let cool at room temperature. When first layer is set, pour plain Jello on top. Refrigerate until set. Repeat same for red layer.