Color is often used intentionally in movies. I found it interesting that in Frozen the color palette for the winter dress that Anna bought in Oaken's store is similar to Elsa's coronation dress. I don't know why the producers of the movie decided to depart from what seems like Anna's standard green palette.
This is discussed in the "Art of Frozen" book.
[Michael] Giaimo is an extremely analytical designer, and when he imagined the costumes for the characters, he applied rigorous aesthetic standards. "For Anna's travel outfit, I wanted something that would be really striking and bold, yet elegant," he begins. "She's a princess, and that really blue skirt says royalty, as does the magenta cape. I thought those two colors would be really striking, because there's a rich saturation to both of them. But there's always a little bit of black on the characters: it helps anchor the saturation, so it doesn't float into the atmosphere."
The warmer green palette was reserved for Anna as she grew and reflected her "sunny disposition". Obviously by the point in the film that she's changed clothes, her disposition is slightly more reserved.