Agree on the green olives, when bought here. Most black olives we can buy (if not located in the Med or similar climate) are green ones oxidised, which then turns them black.
But black olives from source like Yagli Sele though, are less salty than our brine soaked imitators (and much less salty than me) and taste great. As does the Greek Kalamata which is much fruitier than any black olive you'll eat in the UK. Mind I've not had them for ages, I was last in Greece nigh on 7yrs ago
Will get the Yagli soon though. Great to have with a pint!