It's possible the posters have been re-produced badly by whoever uploaded/has been spinning these round the web. Julias hair is two different colours, actually they have two different colour saturations by the looks of it, so I'd wait to you see the poster on wall somewhere before deciding on the colouring.
I've said this before but the movie will do fine, it's not going to break any records but it'll find it's own little niche market. A film that can neatly cover material for kids or tweens whilst making it bareable for accompanying adults has a reasonable chance of survival.