Launch PowerPoint 2011 and you will typically see the Presentation Gallery — you can accept the default Theme that shows up first or even click the Cancel button in this gallery to open a blank presentation with a new slide based on the same default Theme. When you type text within the placeholders of this slide, the text shows up in black over a white slide background. Most of the time this default look works, but you can change the defaults to something else — for example, you can use any other PowerPoint Theme, including a custom Theme as the default.
Learn how to change the default Theme in PowerPoint 2011 for Mac.

