In the Wonder Woman trailer, we could obviously see that color is a large part of the movie’s storytelling.
First of all, we have Themiscyra, from what is logically the beginning of the film.
Themiscyra is filled with bright and vibrant colors.
Whereas, the moment where we enter Man’s world, things change. The color is muted, with dark tones.
Effectively emphasizing the contrast between the beauty of Themiscyra and the ugliness of man and war.
And, if my theory is correct, and provided that the scenes follow a chronological order, the darkening of the colors represent Diana’s gradual loss of faith in man.