There are three areas of traditional overshot: pattern, background and halftones. When the pattern weft does not float above or below the rest of the fabric, but is woven in just as the tabby shots are, we call these areas halftones. This over-under alternation of your pattern weft ties the pattern weft securely to the ground cloth.
Notice the halftones on both side of the solid block. The solid white blocks are the background, the solid red the pattern blocks, and the 'spotted' blocks are the halftone block.
This awesome example is by Jeff Reynolds (Best of Missouri Hands),.