In the Cerignola olives, you can find three different colors: green, black, and red! The green taste the best imo. The black grow in an area in Italy on top of volcano ash which explains the color.
There are also Maddelena olives from South America which are purple. Very tasty, although a little too strong for people new to olives.
They literally come in all kinds of shapes and sizes. There’s these tiny brown olives from France whose name I can’t remember off the top of my head but they’re about the size of blueberries.
Olives are great. I worked with them for over 7 years.