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What is more, your line of thinking is a good one.
Edward Said constructed basically this same argument - persuasively, I think - in Orientalism, his book on the history of western writing about the east (https://en.wikipedia.org/wiki/Orientalism_(book)). If you can get a copy, I recommend it strongly: as you can no doubt see, the consequences of this idea are extraordinarily complex. For instance: what exactly determines Whiteness, if it's a concept that is defined only as "not-ethnic"?
Along those lines, Noel Ignatiev's (note: a controversial figure) book How the Irish Became White details how Celtic immigrants were NOT considered white in the antebellum South. Anyone in America, I think, with Irish or Scots ancestry knows the long history of American racism against the Celts. Ignatiev argues that the Celts 'gained' White status by setting themselves up as anti-Black by becoming strong proponents of slavery and speaking racist ideologies. I found this interesting and persuasive. The historical evidence of horrible and inhuman Irish anti-Black sentiment is obvious, but where other scholars have proposed things like "oh, the Irish came over and were racist just like everyone else" Ignatiev proposes a more universal truth about the way constructions of race interact.