Blood oranges are wonderful if you can get them; they’re much sweeter than regular oranges. In Italy, blood oranges–as oranges and lemons generally–are strongly associated with Sicily. There are actually at least three different types of blood oranges (see Wikipedia). I remember the ones you could usually find in Roman markets were called tarocchi, which were very dark red and very sweet. You can sometimes find imported Sicilian oranges. Another blood orange salad adds fennel instead of olives and onions. I’ve never tried it, but it sounds yummy, too.
Actually, orange salad is more commonly made with regular oranges. They make a more striking dish, as their bright orange contrasts with the black olives. You can also make the salad just with black olives, and skip the onions and parsley, if you like. Even just plain oranges with olive oil (and possibly a bit of white wine vinegar, if you want it tarter) is really nice.