While homemade pesto is super easy to make it will oxidize when exposed to air or heated up. Avocado also browns quickly. If you want your pesto to remain bright green, fill a large bowl with cold water and several ice cubes and set aside. Bring a large pot of water to a boil. Add a pinch of salt and basil leaves and blanch for 15 seconds. Immediately remove the basil from the boiling water and place in the ice water bath. Once cooled, drain. Squeeze the leaves to remove all excess water and lay them on a paper towel. The lemon juice helps combat the avocado from browning but add it quickly before it starts to oxidize.