The Dreamworks website actually details the steps of their production process, and they begin work on storyboards before the visual development (or more likely they have two teams working on each simultaneously). As I'm working on this by myself, I've personally felt like I'd like to capture the look before I work on the storyboards. In order to create good storyboards that make the most of the characters, and tell the story in the way I want to, I feel I need to establish the general idea properly first through my colour studies. Many production designers create separate concept sketches for this sort of thing, for example Mary Blair's work on classic Disney films like Alice in Wonderland and Cinderella:
The aim of this sort of concept work is to work in larger shapes that indicate a solid foundation for the idea, rather than worrying about detail, and to capture the atmosphere and mood of the scene. Nowadays it's also more common to create long comic-like panels that show the whole film and the transitions between the different colour schemes.
This one is from The Incredibles:
The artist here has used strong, geometric shapes to give a clear idea for the feel of the film. Generally in animated films colours are much more vibrant and exaggerated, but there is still variation on which ones are used for certain types of situations; danger/action scenes most often feature warm shades of red and orange, everyday mundane scenes are usually quite desaturated to reflect reality. Fear and uncertainty is usually shown through low lighting, night-time settings or overcast weather, while joy and hopeful scenes are usually bright and vibrant. (Lighting and weather have a huge impact on this as well).
Personally I like the idea of subverting some of the usual tropes, and maybe having bittersweet/happy scenes that take place in low, desaturated lighting, or betrayals that take place in bright weather, etc. (which actually happens in the DB&NG story Photogen abandons Nycteris in the daylight). There's certainly lots of opportunities to experiment and not just use the expected techniques as 'rules'.
I created some rough frames for part of the introductory scene to my film. I have changed the original story a little bit, and instead of having Watho the witch lure two women to her castle so she can steal their children, I've had her find some kind of secret scroll (after years of searching) which is a sort of 'recipe' for crafting a being made from light, and one from darkness. So Photogen and Nycteris are more like her 'experiment' and will have physical characteristics that show them to be unnatural beings that set them apart from ordinary humans (more on that later).
Anyway, so I thought the intro would be Watho finally finding the scroll after a long period of hopeless searching - she enters a gloomy cave within a forest that is lit with a sort of super-natural light which gives the scene a mysterious, magical quality. These purple/green shades are contrasted by yellow/orange lamplight, and also a shaft of light crossing the chest in order to make it stand out from the background. I have also experimented a little with shot composition (where elements of a scene guide your eye to where the focus should be) by having the chest entangled in roots which all curve towards it. The scroll is vibrant and yellow, indicating how Photogen and Nycteris are actually going to be good, moral beings who ultimately defeat Watho, who's pale, blue undertones to her skin and greying hair contrast the scroll and highlight how she has suspect intentions.
I placed a Photoshop artistic filter on the storyboards so that the focus is more on the colours themselves rather than drawing/colouring technique. The first frame is supposed to show Watho, hidden in a cape, walking through the cave with her lantern. She sees the chest, illuminated by light, and approaches it. When she opens it and sees the scroll, she lowers her hood triumphantly to reveal her face and hair fully to the audience.
I will eventually create 'snapshots' of each scene in the film, not in this much detail, and link them together into a long panel like The Incredibles one above to show the transitions between colour schemes.