Harry Potter: 10 Changes From The Books That Ruined The Movies
3. Lily's Eyes
Some changes from the books work much better in communicating the story's message. When Snape dies in print, he merely asks Harry to look him in the eye, whereas on screen he additionally comments, "Harry, you have your mothers eyes," prepping audiences for a massive rug pull. Cut to five minutes later when Harry looks at Snape's memories and discovers the potions' master was in love with his mother all along.
It's an emotional twist, but also completely undoes one of the series' essential running themes; young Lily has the wrong colour eyes. That Harry has his mother's eyes was something commented on by all manner of characters throughout the series and is one of the biggest clues that Rowling knew the major story beats of her narrative from the very beginning. But at some point in the films it got messed up.
Daniel Radcliffe, blue-eyed in real life, didn't wear contacts to turn his eyes green for the role because ramming things in children's eyes isn't OK, even in Hollywood. Fair enough, but then when young Lily was cast in Deathly Hallows they chose an actress with brown eyes. Red heads with blue eyes aren't the most common, but for a massive blockbuster, a proper search is probably worth it. Most perplexing is that choosing a Lily with brown eyes still diverges from the book anyway - her's and Harry's eyes are meant to be green.