First, select an image that features distinctive imagery while at the same time appealing to your artistic taste. A silhouette of several figures or a row of buildings is an easy image to work with. Then, tape a large sheet of drawing paper to the wall, turn on the slide projector and then turn down or turn off the overhead lights. Now place a 35mm slide transparency (or a digital image, if you have a digital projector) into the carousel and turn on the projector. Fix the projector so that is at the same height as the piece of paper and adjust the size of the image so that it fills most of the paper.
Take a piece of charcoal or a soft graphite pencil and trace the outside of the silhouette. This should leave you with two distinct areas, the subject or main figure and the background.
Next, choose a dark solid color for the subject (no need to use black) and a lighter tone for the background. Do this exercise as many times as you like, perhaps varying each attempt, by using different colors or changing the size of the main figure, by moving or adjusting the slide projector.
Set up the projector, and choose an image with large area of strong color. Pick a picture with a sunset, a large field of fresh grass or perhaps just a large expanse of wall. Adjust the image so that it is bigger than the sheet of paper and make sure that it is in focus.
With a set of soft pastels or water-based paints, start applying small areas of color that match the hue of part of the projected image. Mixing and matching color is not a skill that can be mastered right away, so take your time to experiment with color.
As your skill with rendering shape and color increases, experiment with projecting several images onto the same sheet of paper to create a more intricate and colorful picture. This is a straightforward task that is accomplishing by using one transparency at a time to create several overlapping silhouettes.
Approach this task in several ways. The first option might be to project one silhouette, then draw and fill in the shape with a light wash of color. Now let this part dry and then project the next shape onto the paper, so that you can also fill that shape with a different colored wash. Do this as many different times as you like, but be aware that a large number of overlapping images quickly become hard to work with.
The other possibility is to draw the outline, for each sequential shape first, and only begin with the addition of color until you have completed the intersecting outlines of several images. The many small spaces created by the multiple drawings provide for a mosaic of different shapes and colors.