Yes sad but wasn't there a lot of inter marriages between germans in the east and their Slavic neighbors ?
And I live in Chicago ( more poles, serbs, czechs here than Warsaw or Belgrade maybe not sure) and honestly many of them seem more classically "Nordic " then those germans I see in downstate Illinois.
That's kinda one of the classic quips that people mention about Hitler being surprised there was a seemingly greater proportion of blue eyes and blonde hair in Poland than in Germany. And yes, Chicago has the most Polish people of any city in the world aside from Warsaw.
There were a lot of intermarriages, but it appears that more often than not, Slavs were assimilated into German culture rather than the reverse. This is more conjecture than anything, because I have no real way of backing that up, but it's the impression I have got from what I have read. Since German culture was a lot more urbanised than primarily village-based Slavic culture, it was generally more sophisticated at the higher level and encouraged assimilation. That being said, I would say that most people in the Czech Republic at least, if not in Poland too and to a lesser extent in former Austro-Hungarian territory have some German ancestry. German lords may have primarily married German women, but I would be amazed if having Slavic mistresses wasn't extremely common, with the accompanying unrecognised bastards that would be raised as Slavs.
Insofar as one can associate particular ethnic groups or groupings with certain "looks", which always has some problems inherently anyway, there does seem to be an Eastern European "look". To use myself as an example, my father is Croatian but my mother is of an Anglo-Saxon and Scandinavian background, and people constantly mistake me for being either Polish, Russian or Ukrainian, because I'm a lot fairer-skinned than most Yugoslavs but people still pin me as Eastern European. This despite having blue eyes and blondish hair. One thing that always struck me about old Soviet and Eastern European statues is that if they're modelled after a particular figure they're often very true to what they looked like, whilst abstract "Soviet man/woman" figures look German to me. Something to do with statuesqueness of finer cheekbones and stuff probably. Also I don't think that there's been any academic study on it, but I also kinda feel like in a lot of Slavic cultures (and it's more noticeable in older generations) is Nordicist biases despite the fact they aren't included in that, which seems to suggest a favouring of "Germanic" features akin to how African-Americans tend to prefer lighter skin etc.