How to tell if those black olives are real

Are they real or just dyed black?

The colour of an olive that you get from the shop actually has nothing to do with what type it is: Olives are green when they’re plucked unripe from the tree and will change colour as they become increasingly ripe, from reddish brown to dark violet or jet black.

Unripe green olives are firm and taste more mild, while black olives have a more herbaceous note. But whether ripe or unripe, olives are extremely bitter when taken straight from the tree.