>>520825287 (OP)
>Why do some Ashkenazi Jews have clear Euro admixture like blue/green eyes, light hair and light skin while others have the more Semitic browner phenotype? Haven't Jews always been endogamous?
I can't believe you can't find the answer yourself from what you already know.
Jews are Semitic people from the Near East who emigrated to Europe and had their densest settlements in Eastern Europe around Russia and, most of all by far, what today is Poland.
Since Jews lived in Poland and northern Russia for many centuries (since at least AD 1300, after spreading north from the Mediterranean area, where they went first after the Diaspora), of course Jews ended up mixing with the local population.
Put populations side by side and it is guaranteed they will intermix, like a law of probability, so that even if most members of each population don't intermix, some will and, over time, the two populations will share an increasingly amount of DNA in common with each other.
So, Jews, having lived in Eastern Europe around Poland, most of all, but also northwestern Russia and the Baltic region, have acquired genetics, via intermixing, from the native populations of that area, and that area turns out to have the highest concentration of light hair and skin and eyes in the world, alongside Scandinavia, though some studies show an even higher prevalence of blue eyes and blond hair in Poland than even in Sweden.
Hence the blond hair and blue eyes and light skin of so many Jews, especially Ashkenazi Jews, who are the group of Jews who went to northeastern Europe to settle.
But of course the intermixing of an originally Near Eastern population with local Northeastern Europeans wasn't a 100% complete process of intermixing that would have turned each original population into one resulting population of identical individuals, so some Ashkenazi Jews are lighter, in skin and eyes and hair, than other Ashkenazi Jews, since these lighter-featured Jews have more local ancestry.