Once the landscape is drawn in perspective, further depth is achieved through color and shading. A shape composed of a single flat color is only a shape, and lacks form. To achieve the form of a three-dimensional object, there must be a variation or graduation of color across the object.
When choosing color, note that large blocks of strong contrasting color may destroy the sense of depth. It may be decided, as we did when designing our Autumn Aspens sweater, that strong color was an important part of the statement we wished to make. In order for the suppression of depth that was created by placing a strong, vibrant purple in what should have been distant mountains behind the flaming yellow Aspens, we exaggerated the perspective to compensate.