[Major]

"In the popular fairy tales, Snow White is a recurring character in various stories. In one, she has a sister, who also has a color in her name. What is it?"

I believe that would be Rosey-Red. From what I've read online, Rammstein's song Rosenrot was partly inspired by a fairy tale featuring her, as well as a different one (can't remember which one off the top of my head).