In this case, I painted a very thin coat of diluted acrylic paint onto the paper and allowed it to completely dry. Then drew my image onto that orange paper and set about painting the painting using sometimes opaque pigments and sometimes transparent pigments. The results are startling!
Here I have included a landscape with a very dramatic oblique dominance and a brilliant orange underpainting. That orange shows through and helps much of the foliage in the (lower parts of the painting) glow. The opaque gouache used in the sky and a few other spots causes the transparent passages to sing out.
Also, as a class demonstration, the still life (number 103, I believe) was used as a subject. A calmer orange was used in this painting and grays employed to cause the oranges and blue violets to appeal more to the viewer. This piece was literally slapped together to show how the underpainting could be used. Later, line was used through the piece to deliver more texture and interest.