I would revisit this statement you made: "wherea the impoverished immigrants from Europe blended in fairly quickly - just a single generation was all it took..."

All the way into the 1960s Jews, who were of immigrant status and immigrant parents, were refused housing, purchasing automobiles, membership in clubs and associations, entrance onto golf courses, and on and on and on. In 1964 I remember seeing signs up and down the eastern coast, mostly in the South, that read "No Jews or Negroes allowed," and similar wording.

I also do not understand what you meant by this statement: "...When we talk about mixed marriages we are talking about skin-colour not religion..." Again, this was not my life's experience.