What does Vae mean by "she's just my sister, and my sister says purple is charming"?

This song was written by Vae to his girlfriend. Maybe he thought it was too dramatic to explain it to his girlfriend in person. So I borrowed this song to explain it to his girlfriend. Vae didn't want his girlfriend to misunderstand him, so only his sister bought a scarf with him, and he still loved her. As for "Sister says purple is charming", it has nothing to do with the song, but her own opinion. It's just possible that the girlfriend doesn't like purple. Good ... this is my opinion)