Chapter 12 was reprinted after major backlash from readers of her skin tone changing after getting the light spirit king's blessing. Though the original is till up here on mangago. Chapter 13 keeps her original skin tone because the backlash was so sever.
http://www.mangago.zone/read-manga/i_m_not_a_villainess_just_because_i_can_control_darkness_doesn_t_mean_i_m_a_bad_person/nbt/nhs_v-1-chapter-810688/pg-15/
In a way isn't the author kinda using it as a commentary? I mean it wasn't until mc got blessed by the light spirit that she was "accepted", but mc isn't able to accept them b/c of all they had done, since at then end of the day she is who she is. I can't really express myself in words, I'm lacking, but you're right that the end product is questionable.

I’m laughing so hard. The author literally whitewashed their own character with a straight face without thinking that it’s kinda sus? The audacity.
And I’m not talking about this through a “western lens” of racism but the more eastern one where Asians there’s this toxic mindset of valuing light skin over dark; there’s a craziest amount of skin lightening products in Asia. Like skin bleaching is a thing there. The Asian beauty standard is just as insane as it is in America or some other European country. Just because Asian countries (especially Japan) isn’t vocal about their social issues, it doesn’t mean they don’t have it.
Of course, the author isn’t expected to use her manga as a commentary on this social issue but come on. There are ten billion different ways to have the same effect of showing she got the blessing of the light king that isn’t skin bleaching. That’s just glaring for both Western and Eastern audiences.