The phrase "black olives" describes two products that share a colour and very little else. One is a ripe fruit cured in brine. The other is a green fruit turned black by processing. Both are sold under the same two words, and a buyer who does not specify which they mean will, sooner or later, receive the other one.
Naturally black olives
Naturally black olives are harvested when the fruit has ripened and darkened on the tree. They then cure — typically in brine, sometimes dry-salted — over weeks or months, during which the fruit's natural bitterness mellows and the flavour develops. What comes out is variable by nature: colours run from deep mahogany through dark purple to near-black, and no two fruits in a jar are quite the same shade.
That variation is not a defect. It is the visible sign of a fruit that ripened on its own schedule and cured slowly, and in the markets where these olives belong — delicatessen, Mediterranean ranges, premium retail — it reads as authenticity. The texture keeps more bite and more of the olive's own character.
Oxidised black olives
The other route starts with green or turning fruit. The olives are treated in an alkaline solution to remove bitterness and then aerated so that the phenolic compounds in the skin and flesh oxidise and darken. The process is repeated until the fruit is black through, and the colour is then fixed with ferrous gluconate so it holds evenly in the can. This is the California-style black olive, and its defining characteristic is uniformity: an even, deep black, a soft mild texture, and a fruit that slices cleanly and looks the same in every unit.
That uniformity is exactly what the mainstream market wants. Pizza toppings, salad bars and canned retail ranges need an olive that behaves predictably, and the oxidised process delivers that in a way natural curing never will. Calling it inferior misunderstands the job it is doing.