Follow these steps to construct a dummy diagram that you can use to try out effect themes:
Switch to Slide Master view by clicking on View ➪ Slide Master. Go to Insert ➪ Illustrations ➪ SmartArt. The ‘Choose a SmartArt Graphic’ dialog box opens. Click on Cycle and after choosing the top left diagram click OK. A SmartArt diagram appears on the slide master. In the SmartArt Tools Design tab, click Change Colors, and choose the first sample under Colorful. In the SmartArt Tools Design tab, open the SmartArt Styles gallery and select the first sample under 3-D. Now you have a diagram on which you can see the effect themes.