Testing for color blindness
There is a site I ran across recently that will help you see what someone with color blindness will see when they look at your slides. It is at http://www.vischeck.com/vischeck/vischeckImage.php . It allows you to upload a JPG or PNG graphic file and it will show you what people with the most common types of color blindness will see when they view your slide. To use it with PowerPoint, you must first save your slide or slides into the PNG or JPG format. To do so, click on File - Save As. In the Save as type drop down box at the bottom of the dialog box, scroll down until you find the PNG or JPG format. Then click the Save button and decide whether you want to save one slide or all slides if it asks you (usually one slide should be sufficient for this test).
Then you can upload the saved image file and use the tool to see what your slide will look like. It does show you what someone with yellow/blue color blindness will see but my research indicates that this type is so rare that I would not worry about it too much. Use this tool when you know someone with color blindness will be in your audience or when speaking to a large group where the chances are at least some of the people will be affected.