The use of blue in 500 Days of Summer was inspired by Zooey Deschanel’s eyes.
In several scenes of 500 Days of Summer, we can see that the movie’s namesake wears blue dresses, shirts, and skirts. You can also tell that throughout the whole movie the color blue appears many times as a sort of secret code. This, in fact, is far from being a simple coincidence. That’s because the director and the producers found this was the most effective technique to highlight actress Zooey Deschanel’s blue eyes.