Saffron, a delicate yellow-orange spice, comes from the dried, cured stigmas of the purple saffron flower. You'll find it at most grocery stores and specialty food markets.
Heat the broiler. Broil peppers 4 inches from the heat, turning them as their skins begin to blister and blacken, until peppers have blackened all over in a slightly mottled pattern, about 20 minutes. Transfer to a bowl; cover with a towel or plastic wrap. When cool enough to be handled, rub off their skins with your fingers. Cut each pepper in half lengthwise and remove seeds, stem, and membrane. Slice into 1-inch-wide strips. If not using immediately, refrigerate in a glass container.
Heat oil in a large skillet over medium heat. Add onion and cook, stirring frequently until tender, about 10 minutes. Add garlic, paprika, red pepper flakes, and saffron, and cook 2 minutes. Add peppers, vinegar, and olives. Season with salt and pepper, reduce heat to low, and cook another 3 minutes. Stir in mint. Serve.