Another crucial factor is the position a colour will occupy within the room. If it is on the same wall as a window, it will tend to look darker and grayer, especially if the windows are on only one wall. As an experiment, take a large colour swatch and hold it against a wall across from the windows. Next, take that same swatch and hold it against the window wall. The combination of the bright backlight from the window, plus the lack of direct light on the window wall makes the colour look duller and grayer.
South light is crisp and sharp, and it creates strong contrasts within the space. It is a warm light. The perception of colour in a space lit by south light changes continually through the day and even through the seasons. South light tends to be dramatic with pronounced shadows and highlights. If you are trying to play up the sunny character of a south-facing space, muted, warm colours are best so that the colours are not too harsh. For example, a soft creamy, yellow or earthy ochre colour will be easier to live with than a primary yellow.
A bright, south-facing space provides an excellent opportunity to use complex and subtle cool colours. For example, a muted blue-green-gray creates a restful space that is constantly, but slightly, changing with the light. A colour such as this is much like a chameleon. It appears to shift colour, depending on the changing light and in response to the accent colours next to it.
North light is diffuse and cooler. It tends to be more soft, even, and less dramatic. Colours gray down a bit and feel more muted. If your goal is to have a cheerful, sunny, active space, then choose warm colours in lighter values. Contrasting accent colours become more important to give the room some depth and dimension in north light. If your goal is a more quiet, restful, contemplative space, use cooler colours with warm accents. Full-bodied blues and blue-greens appear richer in cool north light. Check your colour samples carefully in the actual ambient light of the room and be sure they don't gray out too much.
East light and west light
It can be a challenge to select colours for a space that has only east or west light. It is helpful to decide if the space is to be used principally in the morning or the afternoon. This way you can tailor the colour selection to the type of light you will most often experience. East- or west-facing spaces are filled with dramatic light in the morning or afternoon, respectively. The sun enters at a low angle and penetrates deeply into the interior of the room. At certain times of day, an east- or west-facing space can be even brighter than a room with a south orientation. At other times of day, the room will be more similar to a north-facing space with cool, diffuse light.
For a balanced colour scheme that works at all times of day, a simple, safe rule of thumb is to use muted warm colours with rich, cool accents. A rule of thumb is a safe jumping-off point in colour design, but as you increase your confidence, try to bend, stretch and eventually break the rules for truly inspirational solutions.
Image courtesy of Pottery Barn.