Powerpoint Transparency

[rowdypixel]

I'm looking to use a projector to show a PowerPoint presentation, but it will be projecting onto a pattern instead of the white screen. Is there any way I can make the background of the slide transparent so the pattern shows through instead of pushing white onto the pattern?

 

[Whatsisname]

Make those areas black.

http://en.wikipedia.org/wiki/Additive_color