Introduce a 'Sketched View' mode, which a designer can toggle on/off. This would effectively remove all color from an artboard/design and render lines,borders,shapes with a slightly hand drawn effect, greyscale images, etc. You may have produced a lovely design but don't want the client to initially get held up on color choices. Once layout tweaked/approved you can then turn off 'Sketched View' and re-publish for the next review stage.