Olive trees are slow-growing, and some of the finest oils come from trees that have been on European hillsides for centuries. The term refers to oil from the first cold pressing of the olives, using the weight of the press alone without any heat or chemicals. Anything higher is inedible. Though darker color can indicate better flavor, color varies wildly among extra-virgin oil, from sunny yellows of some Greek oils to pine greens of some Italian ones. Whether it's a boutique Tuscan oil or something produced the next town over, stick with an oil that tastes great to you and complements your ingredients.
Olive oil is as variable as wine.
When first pressed, it has a spicy-bitter flavor that soon mellows. Although many blended oils taste alike, top producers also make oils so distinctive that experts can tell what groves they came from. If you're serious about oil, use two. For drizzling on finished dishes, spend more for a truly flavorful oil. Your second oil is cheaper, for everyday uses or times when you don't want the olive flavor.