Top 10 Most White U.S. States

After centuries of a race-based hierarchy, with segregation enforced through law for another century after, and with self-segregation still happening today, many racial groups have effectively developed their own communities and cultures. Black and white do describe skin color, but over here skin color often ends up correlating with or outright affecting a person's culture and social reality. (Also, it's important to note that when we say "black" and "white" it's sometimes— though not always— shorthand for "black American" and "white American".) "Act more black" likely meant "act more African-American" in the cultural sense, the same way a German adopting lots of British culture might be told to "act more German" (despite being German).

And you're correct, native people in the US sometimes don't identify as white. Some native people look white due to mixed heritage, but end up facing some of the same obstacles as "native-looking" people anyways (like inherited poverty, or governments seeking to exploit reservation lands). Native identity gets more complicated, and I don't feel qualified to explain it in detail.