@CardiBSlays
I completely disagree with your interpretation, but "interpretation" is the word here. I don't know the author's intent, and neither do you, but what you're interpreting is that the author depiction is "white = good; black = evil". You're not reading the same story as I do.
1. "Turning white" didn't turn her good. It turned the feeling people have about her when they don't know her. This is what happens in real-life by the way: people tend to have a prejudice on others based on the first things they can see about them. Physical appearance and clothing, mainly, are the primary factors that build first impressions. And when someone is racist or bigoted, skin color is going to play a huge part. The author is not saying "black is evil", but "people there have a prejudice that black is evil", for a very clear reason. As in real life, these reasons (founded or not) often blind people to the reality of the specific individual in front of them, and that's what the author criticizes here. Which would mean he agrees with you that society is wrong when judging people for reasons that only go
skin-deep. (yes, pun intended, bad as it is.) You're not going to make many friends in your social wars if you reject those who agree with you.
2. You're making a bad reading of the word "blessing" in this chapter. In our world, a "blessing" is generally synonymous with "good luck". In this manga, a "blessing" is
literally a gift from a magical being, regardless of the intention behind the gift. And the blessing here is not "white skin", it's the healing magic. Case in point, this is still a "blessing" in the version where she keeps her dark skin and that doesn't change the story. Case in point again, she was "blessed" by the Dark Spirit King from birth, but very few saw that as a good thing.
3. Points 1 and 2 above have also mean that "skin color" was never the point. It's about how people in that world take arguments of authority and/or guilt by association to an absurd level.
She was originally "guilty" of nothing more than being chosen by the Dark Spirit King (historically a mass-murderer).
And she's "innocent" now by being chosen by the Light Spirit King (historically the one who stopped mass-murderer above).
Only the people who were directly impacted by her actions have judged her for who she is and what she does. Nobody else changed opinion about her until she gets her new "blessing", and you can bet most of them now judge her positively because of the Light Spirit blessing than because of her actions. This would be made more obvious with a physical change, which is the whole premise of this story.
My conclusion is that you're projecting too much of your own prejudice and/or social trauma on the author to read through the story without outrage on an aesthetic choice.
(nb: I also think the choice is poor, but not for "social justice" reasons.)