Halftone is a simple way to highlight whatever we want (categories, links, worksets, filters..), by softening the surrounding objects, cause you need only one click to lower anything fluently. But it only applies to lines, not faces. If we are working with shaded mode on, all of those objects will remain visually strong, as their shaded colours are not halftoned. The idea is to soften also all colours applied to faces, so then we will be able to truly highlight all not-halftoned objects, easily