Take notes about the colors in your image. Write down the colors of particular objects that you wish to shade. For instance, if you draw or paint an image of a tree, note that green belongs to the dominant colors of your image.
Consult a model of the color wheel. Access images of the color wheel in art books and Internet sites. Find a color wheel model that shows a large array of colors. This helps you narrow down the complement of the exact shades in your image.
Hold the color wheel beside your image. Look for the dominant colors that you noted in the picture.
Place your finger on the color that matches the hue of an image that you wish to shade. For instance, place your finger on blue if you wish to shade an image of the ocean.
Move your finger directly across the color wheel in a straight line, through the center. Look at the color on the wheel beneath your finger. This color represents the complement of the color in your picture.
Blend the two color complements to make a brown shade. If using paints, start with an equal mixture of both colors. Add more of the darker color complement to make the brown deeper or more of the light color color complement to make the brown less intense. If using colored pencils, start with the darkest color complement and add the lighter one on top. For instance, if using yellow and purple, apply the purple before the yellow.
Add shadows using browns formed by the color complement mixture to any area of your image that you wish to darken. Vary the colors in the shadows based on the objects you shade. For example, use green and red to make dark brown for the shadow of a tree. Mix a blue and orange to create a shadow on an orange flower.