apukerma, I am not saying that there were no gentile European converts but having blond hair and blue eyes does not indicate anything regarding ancestry. Regions have a profound effect on physical appearance that is why people from Africa are black, people the Middle East ( excluding the Levant) are darker, people from Europe are generally lighter. Ashkenazi Jews have lived in Europe for over 1500 years so it definitely will have an effect on the physical appearance of Ashkenazi Jews.
Physical appearance does not get affected by living in a region for one or two generations, but certainly over a millennium it will have an effect on the physical appearance of a people.