It's easier to take notes and use highlighters on printed PowerPoint slides that use dark text on light backgrounds. What do you do, though, when you're at the library and the PowerPoint you need to print has light text on a dark background?
Go to File > Print. Before you hit the "Print" button, change the Settings from "Color" to "Grayscale." You should see the colors on the Print Preview on the right flip from the original light text on a dark background to dark text on a light background.
Not only will the printed slides now be easier to mark up, they'll also have used less printer toner. If you'd like to be even more economical (yay, go you!), change the "Full page slides" setting to "3 slides" or more.