But not all of the “black” olives we preferred were quite as they seemed. Many lacked that Kalamata depth of flavour. The reason is that almost all of the cheaper “black olives” sold in cans or jars were – and are – green olives coloured black. If you take unripe olives and treat them with an alkaline solution and oxygen, the colour will gradually darken. A chemical is then used to fix the colour, before they are pitted and canned in brine. The label does not have to mention this little deception, since it is the result of processing rather than dye. Given a choice between fake “black” olives and real green, I’ll take the green, thanks.