Fun dinner party fact: there are no green olive trees! The color of an olive is an indication of its ripeness. Green olives ripen and become black olives. Or rather, they transform from green to light brown, to a vibrant red and purple, to the deepest, darkest black. In general, the darker the olive, the riper it was when it was plucked from the tree.
The Bella di Cerignola, better known simply as the Cerignola, is an olive cultivar from Italy. Cerignola olives are very large, mild in flavor, and may be served either green or cured red or black. The variety, which originates from the south-eastern Italian province of Apulia and is named for the town of Cerignola, is popular for table olives.
Fruit harvest is in November for naturally black ripe olives, but some recipes call for green-ripe olives, which are usually ready in mid-September. The riper the fruit is, the easier it is to bruise the olives, so handle them carefully. Olive trees tend to be alternate bearers, with large crops alternating with smaller crops.
The Picual, also known as Marteña or Lopereña, is an olive cultivar from Spain. Picual olives are the most commonly grown olive today for olive oil production, with production centered in the Spanish province of Jaén. Picual trees are estimated to account for 25% of all olive oil production in the world.