Their colour often tells you a lot about olives

To start classifying the olives, one must first look at their shades. Olives get a different colouring depending on the level of ripening when they are harvested. Each type has different qualities, but all of them are equally delicious.
Here you have some clues to understand this rainbow of colours:

Green Olives from Spain are fruits harvested during the optimum ripening period. They could range from green to a straw-like colour and have characteristic smoked notes.

Ripe black Olives from Spain are harvested before they ripen, and are specially treated for their colour and to eliminate bitterness.

Harvested just before or when they are completely ripe have shades of reddish-black, purplish-black, purple, greenish-black or dark chestnut, with a truly Olives from Spain profound flavour.

Pinkish, wine-red, or chestnut-collared Olives from Spain are semi ripe fruits, harvested before they have completely ripened.