Not to give Blazing a coronary or anything but out of curiosity I looked up the video where Taeyeon says the Alicia Keys thing and I think she does actually say "pretty for a black person".

Though I can understand where the "black friend is pretty" thing came from cause she said the word "chigo" which afaik is slang for something that's out of the ordinary or unexpected but it could easily be misheard as "chingu". Though my knowledge of Korean is rudimentary at best but even I understood her.
It's not like it changes anything - it was years ago, she learned from it, etc - but that was the first time I ever actually listened to the audio and I'm honestly bamboozled as to how there's still debate about what she said. It was like 4 words, it's difficult to miss the meaning.
EDIT: I could be totally wrong though like idk. I have a friend from Daegu and she heard the same thing I did so I'm inclined to believe the "mistranslation" thing was just fans trying to defend her.