A background that looks great on a PowerPoint slide projected on a screen may not look good when you print it.
If you use strong colors in your background, especially dark colors with light text, colors may bleed, or wick, when you print them, especially on an ink jet printer, reducing legibility. Also, light text is hard to read on a dark background when printed; we’re simply used to black or blue text on white paper. Finally, you’ll use a huge amount of ink.
The solution is to use a special background for your handouts. This background is usually mostly white and moves the image from your background to a bar on the left. Then you use dark text for your print background.
An easy way to do this is to complete your presentation and then make a copy of it. Change the background and change the text color in the master from light to dark.