Printed presentations don't match what I see on screen
Your screen and your printer use very different methods of displaying colors. It's not at all unusual for the two to be different.
If you want to get a better match, the first thing to do is check your printer driver settings. Many printer drivers include some sort of color management features that may help. If the driver offers a setting named something like "Match Screen" give that a try.
It may take a good bit of fiddling around with settings and making test printouts to get the results you're after. In some cases, your printer may simply not be able to reproduce the colors you've chosen. Your screen has a wider "gamut" or range of colors that it can reproduce than your printer does, so some colors you see on screen simply can't be printed. Doing so would break the laws of physics, and that would annoy Mr. Newton and all his dead and living friends, so we don't want to do that.
There's another approach to getting predictable printed colors that's more accurate, though.
Instead of trying to get your screen colors to reproduce reliably on your printer, start with printer colors you know you can reproduce and choose screen colors that make them happen.
Microsoft has a handy file that helps. PRINTME is a PowerPoint file that contains a replica of PowerPoint's color picker. All you need to do is open it and print to your printer to get a sample of how each of PowerPoint's standard colors will reproduce--on that printer.
When asked, have your browser save the file to your hard drive. It should only take a short while, since it's only a 25k file. Once you've downloaded the file, locate it in Explorer and double-click it. It will extract PrintMe.PPT, which you can open and print from PowerPoint to get your sample printout of all PowerPoint colors.
When you make the printout, take an extra moment to choose Start, Settings, Printers. Right-click your printer and choose Properties from the pop-up menu. Jot down (on the printout itself, ideally) all of the current color and resolution settings for the printer driver. If you change these, it can affect the colors you get from the printer, so your sample printout may no longer be valid. You might actually want to run a test printout for each of the printer settings you commonly use.
With your test printout in hand, you have a dead-accurate color swatchbook that tells you how each of PowerPoint's colors will reproduce on your printer. Choose your colors from the swatchbook, then pick the corresponding color from PowerPoint's color picker.