I hope this is not too stupid of a question, if it is I already apologize in advance.

Basically my girlfriend and I who are from Germany are planning to travel to the USA. We were hearing stuff that some Americans socially divide people by their ethnicity. I just wanted to ask online whether this is true and if there could be any concerns because my skin is very bright and my girlfriends skin is very dark.

Normally we never really cared or talked about this since at least in our community (where we are from) no one makes a thing out of it and we both just identify as German. But I heard that in some procedures in America you have to say what your ethnicity is? We even heard things like that in some places they divide people by "skin color" and base different cultures on that (we noticed that people from America even speak and behave differently based on whether they identify as "black" or "white") and even have schools for primarily people with dark skin or so. And this concept is v