The background of this 5 x7 watercolor sketch is a fairly strong cadmium yellow that is left to dry. Flecks of the pure yellow can be seen around the edges. The purpose is much like that of using a ground color on a canvas, which provides a unifying hue to all the colors layered over it. Thus the yellow shows through both the red and green. I then painted an ultramarine blue over the red to create the shadow, but because the red was partially wet, it absorbed the blueness. Effects such as these can be done on a small scale to see what happens to the washes before painting a larger version.