How to Keep Avocado G reen?

Did you notice that avocado flesh turns brown very quickly once it exposed to air?I have observe many times because i love to make an avocado shake.Once it turns to brown it do isn't look fresh and nutritious anymore.right?
How can we preserve our avocado fruit flesh?
1.Rub 1 tablespoon of olive oil on all of the exposed avocado flesh
2.Allow the excess oil to drip into a shallow bowl.
3.Then place the avocado half cut side down in the center of the oil puddle creating a seal.