ABSTRACT: The writer analyzes the presence of certain colors which frequently appear in the franchise.
There are many colors in the world, but JK Rowling outlines three in her books. The films take this scheme and amplify it. The colors are Red, Green and Blue.
Red: Red signifies good in this series. It is the primary color of Gryffindor, which is the Hogwarts house of courage and trust. Our general cast of characters are all here. And in the Movies, several of Harry's shirts are Red Sweaters and Harry's Triwizard outfits are all red and black. It should also be noted that both Lily and the Weasleys have Red hair. Similarly, at least in the movies, the Disarming Charm, Explelliarmus, is Red. In the books, it's the color of the Stunning Spell. Other examples include the Red Sparks Spell, The Red Stars and Moon on the clothes that the Hogwarts staff wear at the Third Triwizard Task, The Hogwarts Express (especially when Harry first sees it) and the Sunrise in the Great Hall at the end of Deathly Hallows.
Blue: I know Blue's the color of Ravenclaw, but it is used quite frequently to represent mystery, suspense and an overall feeling of cold. I'm not sure about how much this was utilized in the books (it's possibly tied with an unforgivable curse), but there are tons of examples in the movies. Most obviously the Dark Forest, the Maze, and the Graveyard. The Pensieve in Goblet of Fire is another, and the same with the Movie Triwizard Cup. In fact, even the Goblet itself is blue, and so is the Veil and the whole Department of Mysteries in Order of the Pheonix (and part of the book as well). In fact, to the trained eye of the artist, it's not hard at all to see the bulk of movie 5 was sort of blue-washed, as adding some blue where there was none can desaturate other colors a bit. Examples of that would include Harry's rescue from the Dursleys, the Ministry Hearing, the Room of Requirement, and to a lesser extent, most of Hogwarts since Harry's constantly given the Cold Shoulder. There are likely examples in the other films (Prisoner of Azkaban most likely), but I'll keep it short and sweet. I also realize now that some similar alterations were probably applied to Deathly Hallows Part 1.
Green: This is probably the most interesting, as it's way more obvious. Green = Evil in the books and the films. It exists to give us the sense of fear and forboding. Slytherin is Green. The Killing Curse is Green. The Basilisk is Green. The Chamber of Secrets, at least in the movie, is Green. The merpeople have Green Hair and Teeth. In the movies, the Black Lake is Green, the bulk of Half-blood Prince is Greenwashed (otherwise it'd be all Black and White), and even the light in the Cave is Green in the book.
Connections: Yet another clue to Harry and Voldemort's connection is in the eyes. Actually it's in the Iris's. Voldemort has Red Eyes while Harry Has Green. Since each's iris color is the signature color of their nemesis.