For the dressing, in a jar or small bowl, combine the olive oil, vinegar, orange juice, honey and salt. Add a few grinds of pepper and whisk to mix. Reserve.
Using a sharp chef's knife, cut off the stem end and the opposite end of each piece of citrus to make a flat surface. Place on the flat, cut side and pare away the peel and pith, leaving just the flesh of the citrus exposed. Place each trimmed fruit on its side and slice thinly. Remove any seeds and reserve.
Spread the romaine on a large platter or in individual bowls. Arrange the radicchio and citrus sections on top of the romaine, with the blood oranges on top. Sprinkle with pistachios and, if desired, pomegranate arils. Drizzle with the dressing. Serve immediately.
This bright winter citrus salad goes nicely with a hearty dish of pasta or warm bowl of soup.