Color theory is just colors looking good together. It's not the same as actually lightening the skin.



When artists lighten skin, it's independent of other factors like shading and highlighting and color theory.



Also, no artist worth their salt is going to alter a character's skin for a background when they are the only character in the image and the background isn't at all focal.



Look, I'm not saying the character is whitewashed, just asking why they decided to go with a lighter color