Even though charts are a visual medium, they still contain plenty of text in the form of data labels, titles, legend, axis labels, etc. Whenever you insert a new chart (or any other slide element), the default colors and fonts used are based on the active Theme of the presentation.
To learn more, choose your version of PowerPoint. If we do not have a tutorial for your version of PowerPoint, explore the version closest to the one you use.
Microsoft Windows
Changing Fonts and Other Text Options for Charts in PowerPoint 2013
Changing Fonts and Other Text Options for Charts in PowerPoint 2010
Changing Fonts and Other Text Options for Charts in PowerPoint 2007
Changing Fonts and Other Text Options for Charts in PowerPoint 2002 and 2003
Apple Mac
Changing Fonts and Other Text Options for Charts in PowerPoint 2011
Tutorial Code: 10 12 06
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