Tall stature (note Fate is excluded) - Pale skin - Violet eyes - Black hair.
Power over body gives the Iu significant speed, agility, and strength - they are described as the most elegant of the clans because they look like they're dancing when they fight. Their build is leaner than that of the Ignis and the Aska and they are not quite as tall as those clans. They are also incredibly skilled in the arts (ether and anima manipulation.)
They aren't as durable as the Ignis and the Aska. Taking a heavy hit could be debilitating... if you can hit one.
*Note: Not all clans have a subclan.