Do you know how Roberto has hair? if it's not like Prodigy's for example.
And no, Roberto is not an African-American, because to start he's from Brazil.
And if perhaps this is a schock for you too, but Roberto has always been identified as Latin or multiracial, I advise you to read the first numbers of New Mutants.
Roberto's father was a black man, with all the associated phenotypic characteristics.
Roberto's mother was white and redhead.
So they represent Prodigy.
And that's how they represent Roberto.
I think there are obvious phenotypic characteristics, which make them quite different from each other.
Even in the movie, why was not it represented by someone black? anyway.
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And yes, Monet is not of a specific race, so it has always been and always will be, for something comes from mixed races, and is something very noticeable in it. And marvel wants to leave her like that.
Not understanding and making M a black woman is why, when it is not the truth.