The survivors, called Pearls, suffer from oppression under the new majority of dark-skinned Coals.
The race reversal isn't a new premise in YA by any stretch. UK author Malorie Blackman's NOUGHTS AND CROSSES was published here a decade ago... and to some critical acclaim. From Wiki:

This novel describes an alternate history where humans evolved while Pangaea was still intact. Without the barriers to exchange of domesticable animals, among other factors, the natives of Africa gained a technological and organizational advantage over the humans of Europe rather than the other way around, and made Europeans their slaves. At the time of the story, slavery has been abolished, but Jim-Crow type segregation operates to keep the Crosses (the Africans) in control...

Persephone 'Sephy' Hadley is a Cross (meaning that she has dark skin) and the daughter of a wealthy politician. Callum McGregor is a nought (meaning that he has light skin).
Malorie Blackman describes herself as "a black woman writer", so she's not writing from a position of white privilege. I haven't read either book, so I can't comment on how the subject matter is approached in both or what I perceive the authorial intent to be, but it might be interesting to compare and contrast how perceptions of white privilege might impact on the kneejerk reactions of other people who just hear the premise and haven't read them either.