Open up a new show in PowerPoint (you'll get a blank template slide). Pull down your Tools menu, choose Options, then select the Print tab. Under the section Default Print Settings for this Document, bullet off the option: Use the most recent print settings.
Choose that option provided your last (most recent) show was printed in color. Otherwise, you can force the new show to be done in color (that's the option right below "most recent"). Then, on your next show, choose the "most recent" setting.
That should fix your problem.Edited for clarity.
Edited by txtchr, 27 January 2010 - 04:19 PM.