The inspiration fabric itself doesn't have to be used in the quilt, layout is up to each quilter. It could be used in any position, but consider whether or not it blends too much with the pinwheel blocks, giving them less definition. You could opt to sew borders with the fabric, after first surrounding the quilt top with a narrow, dark 'separation' border.
Pinwheel quilt blocks are made with four half-square triangle units that are dark on one side and light the other. The differing color value makes the pinwheel blocks appear to spin when they're sewn together.
For the event, both fabrics used in a single block were the same color, but one was light and the other was dark. Overall, a wide variety of colors were used, resulting in lovely scrap quilts for the recipients.
The starting point for "dark" and "light" is up to you, but when selecting fabrics for a single block, it's important to choose fabrics that contrast with each other or you'll lose the pinwheel's spin.
To make blocks similar to the ones we used in the forum, sew with tone-on-tone fabrics or choose prints that "read" as (look like) the color you're targeting when viewed from a distance. Avoid true multi-colored prints with no definite color.
Jump to page 3 to find cutting instructions for several sizes of pinwheel blocks.