I am black/Irish, with medium skin, curly dark brown hair, and almost black eyes. My dh is Irish/Scottish, with pale skin, curly dirty blond hair, and blue eyes. Not only do our kids not look like each other, but they don't really look like us either!
My stepson has all dh's coloring but none of his features. Our ods is like a perfect blend of us - light tan skin, curly light brown hair, hazel-y green eyes. Our yds has dh's skin, my dark eyes, and stick straight white blond hair.
We get comments all the time, but always positive. People think it is cool that they look so different, and yet, somehow you can tell they are brothers.
We really emphasized dss's role as big brother during my pregnancies, but we didn't do anything special with him to address that his siblings might not look like him. I agree with the poster who said multiracial and blended families are so common these days, the kiddos don't think much of it. Case in point - when our youngest was born he looked Chinese (yes, the towhead one!). I overheard dss telling his maternal grandmother "I thought it was cool just to have a black brother but now I have an Asian one too. My family is so special!"