So, it definitely is a real thing that's happened. There are a bunch of examples that you could point to that show it. I think it's partly because of how over represented red hair is in media compared to real life. Like, just looking at Disney princesses, you've got Ariel, Merida, and Anna, Giselle, and Megara. Of the 13 Disney Princesses™️ plus some of the common unofficial princesses (I'm counting the two in Frozen, Eilonwy, Esmerelda, Kida, Jane, and Vanellope in addition to those named above), that's over one in five. Far higher than the presence of red heads in American (since we're talking about media produced in America for a primarily American audience) society.

That said, the live action remake of The Little Mermaid isn't even an example of it. They changed the character from white to black, but she's still red-haired. She doesn't have the bright cartoonish red hair of the cartoon. Because...yeah, it's not a cartoon But she has a shade of red hair that can easily be found on actual black people.