Text used within a chart is not really formatted by default, and looks very simple. Note that the font style used is derived from the information available within the Theme or template used for the slides. Now you really should not change the text formatting within your chart unless you have a compelling reason to do so. Even though this default format looks consistent, at times you may want to change the text formatting.
Learn about the Fill and Outline options for the Chart text in PowerPoint 2013 for Windows.

