I think it might be the shading or lighting or some other art term I don't know cause she is noticable a little bit darker when compared to the other girls and her skin looks correct during the sex scenes.
Viewing post in What's the deal with Natasha?!
it's not a shading issue. She's lighter than she was in earlier versions of the game, but her sprite isn't. Granted, it's been a couple updates since I last played, but I actually still have an old version installed and double checked because I thought I was seeing things. Natasha was originally dark skinned, her sister still is, and she mysteriously isn't anymore