This is somewhat of an unclear question. Are you asking how an insider (in the sense of a member of the dominant group) would see racial and ethnic differences in the US? Or are you asking how an insider (in the sense of someone who is within American society -- as opposed to an outsider from another society) would see it? Both of these are plausible interpretations of the question.
From the point of view of a member of the dominant group (whites) I would say that racial and ethnic differences are relatively invisible. White people tend to be able to go through most of their day-to-day lives without having to be conscious of racial differences (unless they live in an area with a really heavy concentration of minorities). Because these "insiders" are members of the dominant group, they are treated as "normal" in most situations and therefore do not really have to experience the racial and ethnic divides at first hand.