How to Make It
In a small saucepan, heat the olive oil. Transfer to a small bowl and crumble in the saffron. Let stand for 10 minutes. Add the orange juice to the saucepan and boil over moderately high heat until reduced to 1/4 cup, about 7 minutes. Add the juice to the saffron oil and let cool.
Using a sharp knife, peel the grapefruits and oranges, cutting off all of the bitter white pith; cut the pith from the clementines. Finely chop the clementine and add to the saffron oil, along with the lemon zest. Working over a large, shallow bowl with the oranges and grapefruits, cut in between the membranes to release the sections. Pour the saffron dressing over the sections and stir gently. Serve.