The color choices in print preview are not all you have to work with. You can get more particular by choosing very specific grayscale settings.
How? With the Grayscale View toolbar and menu.
You get to this menu in normal view, by clicking the Color/Grayscale button on the Standard toolbar.
When you choose Grayscale on this button's menu, your slide shows you in the slide pane how it will look in grayscale, and the Grayscale View toolbar appears. The animation shows all this.
The Grayscale View toolbar settings control the grays either on your slide background or on the slide objects, such as shapes, graphics, or even inserted items like a video file. To see how, read on.