Paper Painting: need help on prep work

One of the things Elizabeth St. Claire Nelson suggests in her paper painting DVD (and on her blog) is that you do an "underpainting" in acrylic to help layout composition and lights and darks.

One of my biggest problems in getting started in this amazingly fun medium is picking SIMPLE and engaging subjects without getting too complex.

I am working 11 x 14 on YES canvas board. Elizabeth's backing of choice is birch boards 9 x 12 with a clear coating. She uses a very watery acrylic mixture for her under paintings so that pencil lines will show through. They are after all mostly going to disappear once the torn paper collage goes on over them. Since the canvas is pre-primed with gesso, I do not have to do any prep work on the support. But you do miss seeing the wood grain that shows in some of her paintings so that I think that some time I would like to try the wood.

I am not using a photo actually, except to look at a photo of a ceramic teapot. And I am not using local color. So this is an exp

eriment in color and design as well.

I am fond of the blue/yellow combination but I am needing some suggestions about a simple background and also some ideas about adding a third color. I usually like to use a triad of some sort. I am thinking perhaps something in a reddish violet.

I am not thinking of adding any other objects but maybe even stamping something in the background or dripping some color into the background. In my original sketch I had some darkness in the right top corner to balance the pot. I like to paint my papers as I choose the colors rather than the other way around. Once I do the underpainting and know the colors I am using, THEN I paint the papers. So what is my third color, guys?